Propeller separation, Lake Central Airlines, Inc., Allison Prop

Propeller separation, Lake Central Airlines, Inc., Allison Prop

Propeller separation, Lake Central Airlines, Inc., Allison Prop-jet Convair
340, N73130, near Marseilles, Ohio, March 5, 1967
Micro-summary: All four blades of the right propeller on this Convair 340 separated
in flight and one of them damaged the fuselage.
Event Date: 1967-03-05 at 2007 EST
Investigative Body: National Transportation Safety Board (NTSB), USA
Investigative Body's Web Site: http://www.ntsb.gov/
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AIRCRAFT ACCIDENT REPORT
LAKE CENTRAL AIRLINES, INC.
ALLISON PROP-JET CONVAIR 340
N73130, NEAR MARSEILLES, OHIO
MARCH 5, 1967
NATIONAL TRANSPORTATION SAFETY BOARD
DEPARTMENT OF TRANSPORTATION
WASHINGTON D C 20591
1IMIOHAL TBAlISrnRrATION SAFETY BOARD
DEPABIMEBT OF TRANSPOBTMION
WASHINGTON, D.
c.
IAKE cmm AIHLIHES, HIC.
ALLISON PROP-JET CONVAIR 340
N73130, XZAR WXEILLFS, Om0
MUCH 5, 1967
TABLE OF COBTtBTS
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Synopsis
Probable Cause
History of t h e P l i g h t
I n j u r i e s t o Personnel
Damage t o t h e Aircraft
Other Damage
Crew Information
Aircraft Information
Meteorological Conditions
Aids t o Navigation
Communications
Aerodrome and Ground F a c i l i t i e s
Flight Recorders
Wreckage
Manufacturing and Related Information
Fire
Survival Aspects
Tests and Research
Analysis
Conclusions
( a ) Findings
( b ) Probable Cause
t
. . .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
...... . . ... . .
SA-395
F i l e No. 1-0001
IMICMAL TEABSPOETATION SAFETY BOARD
DEPAJGMEHT OF TBAMSPORTATION
ASCBAFT Accmm BEPORT
26, 1968
Released:
LAKECEBTFALAIRLUnE, Ric.
ALLISON PROP-JET CONVAIR 340,
W3130, NEAR b%IFSEILLE, OHIO
MARCH5, 1967
SYNOISIS
About 2007 e.s.t.,
on March 5, 1967, .Allison Prop-Jet Convair
340,
1173130, being operated a s Late Central Airlines, Inc., Flight 527, crashed
near Marseilles, Ohio.
injuries.
The 38 persons aboard t h e a i r c r a f t received f a t a l
The a i r c r a f t was destroyed.
Investigation revealed t h a t all four blades of t h e r i g h t propeller
separated i n f l i g h t and t h e No. 2 blade penetrated t h e a i r c r a f t fuselage
i n l i n e with t h e propeller plane.
The penetrations destroyed t h e s t r u c t u r a l
i n t e g r i t y of the fuselage t o an extent that, together with t h e loads caused
by a r i g h t yaw which accompanied the propeller separation, the fuselage
f a i l e d along the l i n e of penetrations and t h e a i r c r a f t crashed.
Examination of t h e i n t e r n a l mechanism of t h e r i g h t propeller revealed
t h a t the h e l i c a l splines of t h e torque piston of t h e No. 3 blade p i t c h
change u n i t were worn away and. t h e torque cylinder was completely f a i l e d .
The wear of the splines was due t o a r omission of n i t r i d i n g f o r surface
hardness during manufacture and t h e cylinder f a i l u r e was caused by fatigue.
- 2When the torque cylinder failed, propeller oil pressure maintaining
the pitch position of the right propeller blades was lost. The blades
moved toward low pitch at a rate too rapid for the propeller pitch lock
to operate effectively. At a low blade angle the propeller oversped,
causing the blades to separate In overstress.
The Safety Board determines that the probable cause of this accident
was the failure of the right propeller due to omission of the torque piston
nitriding process during manufacture, and the failure of manufacturing
quality control to detect the omission.
-31. IKVESTIGATION
1.1 History of the F l i g h t
On March 5, 1967, Lake Central Airlines Flight 527 was a scheduled
passenger operation between Chicago, I l l i n o i s and Detroit, Michigan, v l t h
i n t e m e d i a t e stops a t Lafayette, Indiana, and Cincinnati, Columbus, and
Toledo, Ohio.
The a i r c r a f t u t i l i z e d was Allison Prop-Jet Convair 340, 1173130.
Flight 527 l e f t Chicago a t 1704
and progressed with no reported d l f f i -
c u l t y t o Columbus where it arrived a t 1935.
It departed Columbus f o r Toledo
1 7 minutes l a t e r , operating on an Instrument Flight Rules (2FB) f l i g h t plan
and clearance i n instrument weather conditions.
About 2005 t h e f l i g h t was cleared from i t s assigned cruising a l t i t u d e
of 10,000 f e e t t o descend t o 6,000 f e e t , and t o report leaving 8,000 and
7,000 feet.
Crew achowledgement of t h e clearance and a report t h a t t h e
f l i g h t was leaving 10,000 f e e t was t h e l a s t transmission from the a i r c r a f t .
A t 2007 t h e radar t a r g e t of the a i r c r a f t , which was being observed by
levela and*^^^^^
(Air Route Traffic Control c e n t e r ) , disappeared from t h e
c o n t r o l l e r ' s radar scope.
At tunes variously estimated as between 2005 and 2010, persons i n t h e
v i c i n i t y of Marseilles, Ohio, heard sounds from an a i r c r a f t .
descriptions of sounds were:
Some of t h e
" l i k e an engine revving up," " l i k e a c a r stuck
on ice" and " l i k e a sports car on a drag s t r i p . "
It was reported t h a t a few
seconds l a t e r t h e r e was an explosion l i k e sound and a f t e r another short i n t e r v a l t h e sound of a heavy Impact.
y
It was soon determined t h a t an a i r c r a f t had
A l l tunes a r e eastern standard based on t h e 24-hour clock.
- b crashed and by about 2100 it was established t h a t t h e a i r c r a f t was
Lake Central Flight 527 and t h a t all 38 persons, 3 crew and 35 passengers,
aboard had been Tfllled.
The crash location was 2 miles southwest of
Marseilles a t north l a t i t u d e 4O441'25" and vest longitude 38'21'58".
Witnesses reported t h a t weather conditions a t the time and place of
.
the crash consisted of a low overcast with poor v i s i b i l i t y i n rain, freezing
rain, and snow.
Because of these weather conditions none of the witnesses
saw t h e a i r c r a f t before it crashed.
1.2
I n j u r i e s t o Personnel
Crew
-
InJuries
1.3
Passengers
Others
fatal
3
35
0
Nonfatal
0
0
0
None
0
0
Bwage t o t h e A i m r a f t
The a i r c r a f t was destroyed.
1.4
Other Damage
None.
1.5
Crew Information
Captain John W. Horn, age 45, held a i r l i n e transport p i l o t c e r t i f i c a t e
No. 314457 with C-46, D2-3, CV (Convair) 240/340/4b0 and Allison Prop-Jet
CV 3'40 ratings.
He s a t i s f a c t o r i l y completed a CV 340 f l i g h t proficiency
check September 10, 1966, an Allison Prop-Jet CV 340 f l i g h t proficiency
check August 24, 1966, an Allison Prop-Jet CV 3 h l i n e check September 9,
1966, and an en route check March 1, 1967.
He held a f i r s t - c l a s s medical
c e r t i f i c a t e with no limitations issued November 29, 1966.
- 5 Captain Horn had accumulated a t o t a l of 22,425 flying hours, of which
403 were in t h e Allison Prop-Jet CV 340.
During the 90-day period preceding
t h e accident, a p a r t of which period he was on vacation, Captain Horn flew
151 hours.
He was off duty 85 hours before F l i g h t 527 and h i s duty time i n
connection with the f l i g h t was about 6 hours.
F i r s t Officer Roger P. Skillman, age 33, held a i r l i n e transport p i l o t
c e r t i f i c a t e No. 1222045. with a D2-3 r a t i n g and commercial privileges, a i r plane multi and single-engine land.
He s a t i s f a c t o r i l y completed an Allison
Prop-Jet CV 340 f l i g h t proficiency check December 17, 1966, and an Allison
Prop-Jet CV 340 l i n e check October 28, 1966.
He held a f i r s t - c l a s s medical
c e r t i f i c a t e with no l i m i t a t i o n s issued September 26, 1966.
F i r s t Officer Skillman had accumulated a t o t a l of 4,166 f l y i n g hours,
of which 250 were i n t h e Allison Prop-Jet CV 340.
He was off duty 80 hours
before Flight 527 and h i s duty time i n connection with the f l i g h t was about
6 hours.
F l i g h t Attendant Barbara Littnan, age 23, was employed by Lake Central
Airlines August 3, 1965.
Her l a s t recurrent t r a i n i n g was s a t i s f a c t o r i l y
completed November 1, 1966.
1.6 A i r c r a f t Infomation
The a i r c r a f t was manufactured by the Consolidated Vultee A i r c r a f t
Corporation November 3, 1952, a s a Convair-Liner 340-31.
It was converted
t o an Allison Rop-Jet Convair 340 i n accordance with Supplemental Type
C e r t i f i c a t e No. SA.-4-1100 by Pacific Ainnotlve, Inc.,
of September 13, 1966.
with a completion date
The conversion included i n s t a l l a t i o n of Allison m v i s i o n
6
-
of General Motors Model 501-D13D engines with Allison Division Aero Products
Model A6441 FM-606~propellers.
Lake Central Airlines, Inc., became the
omer and operator of t h e a i r c r a f t September 15, 1966.
At the time of t h e accident t h e basic airframe of the a i r c r a f t had
accumulated 16,216 f l i g h t hours.
Engine and propeller operational h i s t o r i e s
were a s follows:
Position
Engines
Date of
Manufacture
arch 30, 1966
1
Hours Since
Overhaul
S e r i a l No.
Total Hours
CAE 501594
1055
N/A
(new)
P-987
372
N/A
(new)
P-984
1055
N/A
Propellers
1966
1
A U ~ U S12,
~
2
J u l y 29, 1966
Computations showed, t h a t a t departure from Columbus, Ohio, t h e gross
takeoff weight of iPI3130 was 50,626 pounds, t h e maximum allowable gross takeoff weight was 53,200 pounds and the center of gravity of t h e a i r c r a f t was
within limitations.
N'i'3130
was l a s t serviced with 560 gallons of kerosene
a t Cincinnati, Ohio, which brought the t o t a l f u e l load. t o 10,120 pounds.
During the intermediate stops of Flight 527 the f l i g h t crew made no
request f o r maintenance on t h e a i r c r a f t and none was performed.
1.7
Meteorological Conditions
A t t h e time of the accident a cold f r o n t with waves extended south-
westward from southwestern Pennsylvania through c e n t r a l Arkansas and beyond.
2j
Overhaul time f o r t h e propellers a t t h e time of the accident was 2500 hours.
-21
-7Associated with the front, widespread, areas of Ohio, including the accident
location, were dominated by 300 t o 500 f o o t overcast c e i l i n g s and 2 t o 5 mile
v i s i b i l i t i e s accompanied by freezing r a i n o r freezing d r i z z l e and snow.
Weather was no f a c t o r i n t h e accident.
1.8 Aids t o Navigation
Not involved.
1.9 Communications
Communications were n o d .
1.10
Aerodrome and Ground F a c i l i t i e s
Not involved.
1.11 Flight Recorders
The a i r c r a f t was equipped with a Urrited Coti t r o l Corponrtion Model F-542
f l i g h t recorder.
The u n i t -was recovered and it was determined t h a t it had.
functioned normally.
The recording medium had not received any mechanical
damage i n t h e crash.
A readout of t h e recording medium shoved t h a t about 14 minutes a f t e r
l i f t - o f f from Columbus t h e a i r c r a f t had descended from 10,000 f e e t t o 8,000
f e e t and was on a magnetic heading of 322 degrees, with an indicated airspeed
of 254 knots.
The recorder readout showed t h a t a t t h i s time t h e a i r c r a f t
veered sharply t o the r i g h t of heading nearly k0 degrees and immediately
veered back t o t h e l e f t about 55 degrees.
E l e c t r i c a l power t o t h e recorder
was then abruptly terminated.
The a i r c r a f t
Recorder.
Â¥waequipped
with a United Control Corporation Cockpit Voice
The u n i t vas recovered and the recording medium was found undamaged.
-8FTayback of the recording tape revealed t h a t substantial portions of
the crew conversation and radio transmissions were unreadable, but there
was s u f f i c i e n t intelligence t o determine t h a t operation of t h e f l i g h t proceeded n
o
w u n t i l a f t e r descent begm from 10,000 f e e t .
e l e c t r i c a l power t o t h e recorder was abruptly terminated.
At 2006:05
Two and one-
half seconds before t h i s a sound could be heard on the CAM (cockpit area
microphone) c h a m e l a i c h began a s a low pitched h m and increased rapidly
i n p i t c h u n t i l it abruptly stopped with t h e power f a i l u r e .
The sound was
similar t o t h a t of an a i r r a i d s i r e n during Its f i r s t seconds of operation.
1.E Wrec!mge
Investigation revealed t h a t t h e a i r c r a f t crashed i n an upright, nearl e v e l a t t i t u d e on a magnetic heading of a p p r o x h a t e l y 360 degrees.
When
the a i r c r a f t struck t h e ground, t h a t portion of the fuselage ahead of
fuselage s t a t i o n (P.S.) 193 was completely separated, except f o r the cont r o l cables and t h e main e l e c t r i c a l wiring bundle.
Evidence shoved t h a t
the separated forward, fuselage section broke f r e e on impact and s l i d about
90 f e e t ahead of t h e main body of t h e a i r c r a f t .
Examination of t h e main wreckage revealed t h a t a large portion of the
fuselage structure, i n t e r i o r equipment, and furnishings from between F.S.
and F.S.
193
3k0, a length of about 12 f e e t , and t h e r i g h t propeller were missing.
The missing structure, i n t e r i o r equipment and furnishings were found, i n
numerous pieces along a ground path 112 mile wide and 1-112 miles long on
a magnetic bearing of 135 degrees from t h e main wreckage s i t e .
The four
propeller blades of t h e r i g h t propeller were detached and found a t separate
locations ranging from 2,000 t o 2,300 f e e t southeast of t h e main wreckage.
The main reduction drive gear of t h e r i g h t propeller was recovered 2,200
f e e t south of t h e wreckage s i t e .
The r i g h t propeller feathering reservoir,
feathering motor and master gear were found 2,000 f e e t north of t h e wreckage
s i t e and t h e No. 3 torque piston vas located about 300 f e e t west of t h e main
wreckage.
The r i g h t propeller hub containing t h e other three torque u n i t
assemblies was recovered 2,800 f e e t north of t h e main wreckage.
The majority of pieces of fuselage s t r u c t u r e missing from t h e main
wreckage were recovered and a mockup of the forward fuselage a r e a was constructed.
This revealed a v e r t i c a l l i n e of s t r u c t u r a l separation a t F.S. 216
'
which is located i n l i n e with the propeller planes.
fuselage
On t h e r i g h t side of t h e
the mating edges of t h e fuselage skin pieces and s t r i n g e r s along
the l i n e of separation from horizontal s t r i n g e r (H.S.)
9 t o H.S. I T were rolled.
inward and upward, with heavy scuff marks on pieces of t h e i c e s h i e l d from the
same area.
From H.S. I T t o H.S.
21 on t h e same side of t h e a i r c r a f t , t h e
mating edges of fuselage s t r i n g e r and skin pieces were r o l l e d outward and
upward with heavy scuff marks on t h e inside of t h e fuselage skin.
In t h i s
area the l i n e of separation was sharp and narrow with s l i g h t b u r r s pointing
outward and upward.
The c h a r a c t e r i s t i c s of the l i n e were those of a c u t t i n g
penetration by a sharp object.
Between H.S. 9 and H.S.
17 t h e penetration
was from outside t o inside and upward, and between H.S. 17 and H.S.
was from inside t o outside and upward.
21 it
Structure on e i t h e r side of the
separation l i n e from F.S. 193 and F.S. 340 was torn away i n l a r g e pieces
along random l i n e s .
-31
Left and r i g h t a r e looking forward from behind t h e a i r c r a f t .
- 10 On the l e f t s i d e of the a i r c r a f t between H.S.
17 and H.S. 22 a t F.S.
212 the fuselage skin and s t r i n g e r s were broken i n an i r r e g u l a r pattern by
an object moving from inside t o outside.
From F.S.
193 t o F.S. 340 t h e
fuselage skin was torn away i n t h e sane manner a s t h a t on the r i g h t side of
the fuselage.
Examination of equipment and structure from t h e i n t e r i o r of the fuselage
revealed t h a t the upper cargo bin inside bulkhead was crushed inward ( t o t h e
l e f t ) a t a point 27 inches above t h e cabin f l o o r l i n e .
The top cover of t h e l i q u o r k i t , which was positioned on t h e buffet
serving counter about l e v e l with H.S. 19 on the l e f t side of t h e fuselage,
was buckled in ( t o the l e f t ) and there was a semicircular inpact imprint i n
it.
The imprint matched t h e curvature of t h e side of t h e b u t t end of a
propeller blade.
A bundle of 26 e l e c t r i c a l wires, containing t h e power source wires f o r
t h e cockpit voice and f l i g h t data recorders, which i s routed below the cabin
f l o o r close t o H.S. 9 on t h e r i g h t side of t h e a i r c r a f t , was cut a t a location near F.S. 216.
A second bundle of three e l e c t r i c a l power feed cables
which power the 26V DC e s s e n t i a l bus and which i s routed through the same
area, was a l s o cut near F.S. 216.
The a i r c r a f t control cables, however,
which a r e routed j u s t below t h e above described e l e c t r i c a l wiring bundles,
had not been touched by t h e c u t t i n g medium but were broken by overstress.
A n exemination of the four blades of t h e r i g h t propeller revealed t h a t
a l l were f a i l e d i n t h e blade root section, a t t h e sane location and. i n the
-11same manner.
The f a i l u r e s were determined by visual and metallurgical
examinations t o have been t e n s i l e overload type separations.
Examination of the No. 2 blade disclosed it was heavily scuffed on t h e
t h r u s t side in t h e area of t h e t i p , and there were black deposits Impregnated
i n t h e scuff narks.
Laboratory examination of t h e deposit material revealed
t h a t it was of t h e same composition a s the faying s t r i p used between the i c e
shield and fuselage skin of t h e a i r c r a f t .
The propeller torque u n i t assembly serves as a means of converting prop e l l e r hydraulic o i l pressure i n t o mechanical r o t a t i n g o r twisting movements
t o c o n t r o l blade pitch.
There i s a separate torque u n i t f o r each blade.
A master gear t i e s together and coordinates the functions of the individual
u n i t s t o maintain precisely t h e same pitch of a l l propeller blades.
It a l s o
provides redundancy f o r t h e system, i n t h a t i f one torque u n i t were t o f a i l
t h e function of t h e f a i l e d u n i t would be transferred t o and performed by
the others.
The torque u n i t c o n s i s t s of three basic parts:
torque piston, and the torque piston cylinder.
t h e f i x e d spline, the
The f i x e d s p l i n e i s bolted
t o t h e propeller hub and has external h e l i c a l splines which mate with i n t e r n a l
splines on the torque piston s k i r t .
Incorporated on t h e torque piston s k i r t
a r e external h e l i c a l s p l i n e s which mate with splines on t h e inside of t h e
torque cylinder.
Through these splines, l i n e a r movement of t h e torque piston
r o t a t e s t h e torque cylinder and propeller blade attached t o it t o t h e desired
blade angles.
An increase i n propeller o i l pressure moves t h e piston outward
t o increase blade angle and, conversely, a decrease in o i l pressure permits
t h e normal aerodynamic twisting moments of t h e propeller blades toward low
pitch t o decrease the blade angle.
One of the s a f e t y devices incorporated i n t o t h e propeller system, which
is pertinent t o t h i s accident, is the propeller p i t c h lock.
I h i s is a revo-
l u t i o n s e n s i t i v e mechanical device which functions t o a r r e s t propeller blade
pitch-change if t h e propeller revolutions per minute (r.p.m.)
increase t o
v
1055, as opposed t o the normal r.p.m.
which r w i n s e s s e n t i a l l y constant a t
Examination of the No. 3 torque u n i t of the r i g h t propeller revealed
t h a t the i n t e r n a l and external h e l i c a l splines of t h e torque piston were worn
away t o the extent t h a t t h e piston could not function, and was, i n effect, a
f r e e piston.
Subsequent metallurgical a m i n a t i o n showed t h e wear was due
t o a lack of n i t r i d i n g of t h e splines f o r surface hardening.
In addition,
t h e examination disclosed t h a t t h e torque piston cylinder had f a i l e d .
Visual
and laboratory examinations showed t h a t the f a i l u r e was a f a t i g u e f r a c t u r e
which had originated on t h e inside of the cylinder wall and then progressed
around t h e e n t i r e circumference of the w a l l u n t i l a sudden and t o t a l separ a t i o n of the cylinder occurred.
An X-ray of t h e pitch lock and master gear assembly of t h e r i g h t pro-
p e l l e r , made before the u n i t was disassembled, revealed t h a t t h e pitch lock
piston block-out lug was against t h e master gear lock block-out cam, a position
which corresponded t o a propeller blade angle of 21.5 degrees.
This compares
t o a normal blade angle, f o r t h e operating conditions l a s t r e f l e c t e d by t h e
f l i g h t recorder f o r F l i g h t 527, of 49 degrees.
The p i t c h lock piston gear
- 13 t e e t h were badly damaged over an a r c of about 120 degrees and t h e mating
t e e t h on t h e master gear were damaged i n a s i m i l a r manner.
The master gear assembly of t h e r i g h t propeller had. separated from
t h e hub a s a r e s u l t of overload f a i l u r e s of t h e master gear assembly-to-hub
retaining bolts.
1.12-A
Manufacturing and Related Information
On o r about February 27, 1967, a propeller from an Allegheny A i r l i n e s
Prop-Jet Convair was received f o r r e p a i r a t t h e Allison f a c i l i t y with t h e
complaint t h a t it f a i l e d t o reverse.
On March 2, the propeller was d i s -
assembled and found t o contain two torque pistons with badly worn h e l i c a l
splines.
The next day, metallurgical examination determined t h a t t h e splines
on both pistons had not been n i t r i d e d f o r surface hardening during manufacture.
The propeller had accumulated 454 hours i n service since new.
As soon a s t h e defective torque pistons were found, t h e p o s s i b i l i t y
t h a t others might he i n service was realized.
An Immediate search of heat
t r e a t ( n i t r i d i n g f o r hardness) and f i n a l inspection records was made t o
i s o l a t e any other torque pistons which could have missed the n i t r i d i n g process.
By comparing dates t h a t c e r t a i n torque pistons vent through t h e
n i t r i d i n g process, when they received f i n a l inspection, and t h e i r s e r i a l
numbers, with t h e s e r i a l numbers on t h e defective pistons, a group of 234
suspect torque pistons was established.
It was determined t h a t t h e pistons
i n the group were processed i n several l o t s between February and. June 1966.
- 14 When t h e s e r i a l numbers of t h e suspect pistons were isolated, it was
possible from assembly records t o i d e n t i f y the propellers I n which they were
i n s t d e d and, f r m t h e propeller s e r i a l numbers, t o i d e n t i f y the operators
possessing them.
When t h e suspect torque pistons were i s o l a t e d and operators possessing
them were known, it was decided t o i n s t r u c t the operators t o perform a s p e c i a l
check of t h e o i l i n the affected propellers f o r metal contamination.
It vas
reasoned t h a t , since t h e propellers were equipped with magnetic drain plugs
designed t o pick up metal p a r t i c l e s t o show abnormal wear of i n t e r n a l parts,
such an inspection would a l s o reveal metal p a r t i c l e s from the wear of a s o f t
(non-nitrided) torque piston.
On March 3, a l l of t h e affected operators were
telephoned and asked t o perform t h e o i l inspection.
They were asked t o check
the magnetic drain plug and t h e propeller regulator f i l t e r f o r any metal
p a r t i c l e s , t o drain the o i l and look a t it f o r metal contamination discolora t i o n and t o f i l t e r t h e o i l through a s u i t a b l e type f i l t e r t o separate and
reveal any metal p a r t i c l e s i n the o i l .
Only i n t h e l a t t e r respect was t h e
s p e c i a l o i l check d i f f e r e n t from a regular o i l check f o r metal contamination
during routine propeller maintenance.
In the rapid sequence of events t h e
o i l from t h e Allegheny propeller had not been checked f o r metal.
On March k ,
telegrams confirming t h e special check instructions were sent t o all of t h e
involved operators.
When Lake Central Airlines personnel received the special o i l check
instructions and i d e n t i f p n g information a s t o propellers involved, they
determined t h a t t h e four Rrop-Jet Convairs, which were then i n t h e Lake Central
- 15 f l e e t , were subject t o t h e inspection.
Maintenance personnel were advised
of t h e inspection and a form was prepared t o follow and record, t h e check.
On March 4, t h e o i l inspection was performed on M73130.
No metal
p a r t i c l e s were found when t h e o i l was f i l t e r e d through a double p a i n t
s t r a i n e r , and there were no p a r t i c l e s on t h e propeller regulator f i l t e r .
The o i l was green, with no sign of grayishness indicative of metal contamination.
no metal.
The magnetic plug had a f i n e l i n e of carbon-like material on it but
The same material had. been seen before on magnetic plugs during
routine propeller o i l changes and it was a normal finding.
An Allison
technical representative assigned t o Lake Central who, t h e day before, part i c i p a t e d i n t h e s p e c i a l o i l inspection on another Lake Central Prop-Jet,
a i r c r a f t No. 125, considered it a nor&
condition.
It was a l s o the general
view of other Allison personnel t h a t t h e material did not represent metal
p a r t i c l e s expected from t h e o i l inspection i f there were a defective piston.
It vas also noted t h a t subsequent events proved there was no defective
piston i n the propellers of a i r c r a f t 125.
On March
8, following t h e crash of Flight 527, t h e Federal Aviation
Administration (FAA), acting on information obtained from t h e accident investigation, issued an Airworthiness Directive (A.D. ).
The d i r e c t i v e called
f o r an immediate removal of a l l propellers from service i n which torque
pistons i n the suspect range were i n s t a l l e d .
It required t h a t t h e propellers
be disassembled and t h e torque pistons physically checked f o r hardJiess t o
assure they were not defective.
-
16
-
When t h e various actions t o f i n d and remove the defective torque
pistons from service o r p o t e n t i a l service had been completed, 10 torque
pistons had been found which had not been nitrided.
Of
the 10, 2 were
found by the o i l check, 2 were found by a hardness check a f t e r t h e o i l
check had been performed,, with negative results, 2 were discovered in new
propellers by t h e hardness check, 3 were found during propeller maintenance
a f t e r service d i f f i c u l t y and 1 under the circumstances hereinbefore described
r e l a t i n g t o F l i g h t 527.
The manufacture of propeller torque pistons involves 79 separate operations, of which 12 t o 14 were associated with t h e process of n i t r i d i n g the
splines f o r surface hardening.
After several steps of preparation, the
n i t r i d i n g i s accomplished by placing the p a r t s i n a n i t r i d i n g furnace f o r
48 hours a t a temperature of 975 degrees, F.
A s p a r t of t h e o v e r a l l n i t r i d i n g process a f t e r the heat t r e a t phase, a
sample i s checked i n the laboratory f o r case and core hardness, and a depth
check is made of a white layer formed by the nitriding.
The e n t i r e l o t of
p a r t s is then cleaned of the white layer, stripped of c e r t a i n bronze plating,
s t r e s s relieved and additionally cleaned.
The p a r t s then move t o Inspection.
During the above-described operations the l o t of p a r t s is accompanied
by a Process Control Instruction Travel Card.
This card l i s t s t h e steps
t o be performed i n the overall process and makes provision f o r , among other
things, t h e t o t a l number of p a r t s processed, t h e date each step was accomplished and i d e n t i f i c a t i o n of t h e operator involved.
- 17
I n t h e f i n a l inspection phase each of t h e torque pistons i s given a
dimensional inspection, t h e inner and outer splines a r e inspected f o r
surface hardness and t h e p a r t i s magnafluxed.
Each p a r t i s stamped by t h e
inspector involved with h i s inspection identification, f o r each of t h e t h r e e
inspections.
After t h e dimensional inspection the p a r t i s serialized.
In
t h e inspection phase, Inspection and Quality Routing cards accompany t h e
parts, giving d e t a i l e d instructions f o r t h e inspections.
F i n a l Inspection
Records a r e used t o i d e n t i f y the p a r t s involved, the inspections performed,
t h e dates of the inspections and the inspector involved.
The number of
p a r t s i n a specific l o t can be determined from t h e Inspection and Quality
Routing card and checked f o r accuracy by a physical count of t h e number of
p a r t s inspected.
Preceding the Lake Central accident and at the time t h e defective
torque pistons would have been manufactured, t h e splines were checked f o r
surface hardness by means of a f i l e check.
The check was made by applying
a f i l e of Rockwell hardness 89 (BC 89) across the s p l i n e surface.
If the
surface was not of proper hardness t h e f i l e would mark it and one would be
able t o f e e l t h e f i l e drag, but there was no difference i n appearance
between n i t r i d e d and non-nitrided parts.
An Allison Inspector ¥whhad
been engaged i n inspection work more than 15 years and had done some f i l e
checking f o r 7 years, reported t h a t he had, found "soft" p a r t s by using t h e
f i l e check, but never a torque piston.
lighted and not open t o all personnel.
The work area was adequate, w e l l
-
18
-
I n describing h i s work, t h e p a r t i c u l a r inspector involved s a i d it was
h i s habit t o perform h i s inspections, which were both the f i l e and magnaflux
checks, on a l l of the p a r t s i n a l o t and t o then put h i s inspection stamp on
the e n t i r e l o t .
The areas f o r uninspected, inspected, and rejected p a r t s
a r e within h i s work area but c l e a r l y separated from each other.
With respect
t o t h e defective torque pistons, he could not offer any reasonable explanation
a s t o how they could have been s o f t and, if inspected, could have been checked
a s s a t i s f a c t o r y f o r surface hardness.
While it was c l e a r t h a t the 10 torque pistons had. missed t h e n i t r i d i n g
process, extensive e f f o r t s by Allison f a i l e d t o determine exactly how t h i s
omission occurred o r how it escaped detection i n the inspection phase.
One
p o s s i b i l i t y l i e s i n t h e circumstances associated with the movement of 10
torque pistons from t h e production flow t o t h e laboratory in connection with
a s t a t i s t i c a l study.
during nitriding.
The study was t o determine t h e "growth" of t h e p a r t s
I n the laboratory each of the 10 p a r t s was marked with
numerals 1 and 2 a t d i s t i n c t locations on t h e spline. end.
distinguished the 10 pistons from any others.
These markings
Each of t h e 10 defective
pistons was found t o have these distinguishing marks.
A s a r e s u l t of t h e sequence of events and findings a f t e r March 2, a
number of changes o r modifications were made i n t h e areas of q u a l i t y assurance and manufacturing procedures.
pistons p r i o r t o t h e n i t r i d i n g process.
One, was t o s e r i a l i z e t h e torque
This provides a b e t t e r b a s i s f o r
s t r i c t accountability of each p a r t i n the production steps and i n any
necessary acttons whereby p a r t s were moved out of t h e n o d flow.
-
19
-
Another change vas t o put colored medallions i n each container of
p a r t s t o show t h e s t a t u s in t h e production process, and t o mark t h e
medallions t o show t h e precise s t e p i n t h e process such as "carbonize",
" s t r e s s r e l i e f " , "etc."
A procedure t o use the Rockwell hardness t e s t e r a t t h e heat t r e a t and
f i n a l inspections was adopted.
The Roctarell machine can be used on t h e
s p l i n e end of t h e piston only; therefore, it i s t o be used i n conjunction
with the f i l e check.
Associated with t h i s procedural modification, t h e use
of a logbook was adopted i n which t h e specific Roctarell value is recorded
f o r each p a r t by s e r i a l number.
Several modifications o r design changes were made t o t h e 6 0 6 ~propeller
a s a r e s u l t of t h e accident investigation findings and r e l a t e d t e s t work.
-4 1
One was the incorporation of an increase pitch flow r e s t r i c t o r i n t h e increase pitch o i l supply l i n e of each torque piston assembly.
The r e s t r i c t o r
was designed t o r e s t r i c t a l o s s of o i l t o a r a t e which would prevent a decrease of propeller blade p i t c h change r a t e i n excess of 9 degrees per second.
Tests showed t h i s r a t e was well within t h e c a p a b i l i t y of t h e pitch lock t o
control.
Also, t h e torque cylinder was redesigned t o increase i t s fatigue l i f e
from f i n i t e t o i n f i n i t e l i f e under a l l types of f a i l u r e situations.
As a matter of f u r t h e r assurance, t h e pitch lock housing-to-hub r e t a i n i n g
b o l t s were changed from b o l t s with an ultimate t e n s i l e strength of 175,000
pounds per square inch (p.s.i.)
t o ones with a value of 220,000 p.s.i.
addition, t h e number of b o l t s was increased from 8 t o 16.
h/
- See Section 1.15, Tests and Research.
In
- 20 The i n s t a l l a t i o n of the increase pitch flow r e s t r i c t o r s and the
i n s t a l l a t i o n of t h e retaining b o l t s were made the subject of an FAA Airworthiness Directive with a compliance date of November 1, 1967.
While t h e
newly designed torque piston cylinder was considered a product improvement
item, Allison furnished, them t o all affected operators f o r i n s t a l l a t i o n
during compliance with the Airworthiness Directive.
Part 1A5 of t h e Federal Aviation Regulations (FAR) governs Certificated
Repair Stations, and was applicable t o Allison since it was c e r t i f i c a t e d a s
a repair station.
repair station
Under Section .63(a) of t h e Part it s t a t e s t h a t such
". . . s h a l l report t o the Administrator within 72 hours
a f t e r it discovers any serious defect i n , o r other recurring unaimorthy
condition of, an a i r c r a f t , powerplant, propeller, o r any component of any of
then
. . ." Section .63(b) s t a t e s t h a t "in any case where the f i l i n g of a
report under .63(a) might prejudice the r e p a i r station, it s h a l l r e f e r the
matter t o t h e Administrator f o r a determination a s t o whether it must be
reported.
If t h e defect o r malfunction could r e s u l t i n an imminent hazard
t o f l i g h t t h e r e p a i r s t a t i o n s h a l l use the most expeditious method it can
t o i n f o m t h e Administrator."
The f i r s t n o t i f i c a t i o n t o t h e FAA in connection with the aforestated
regulatory requirements was made i n the form of a telephone c a l l t o t h e
FAA Regional office in Kansas City, Missouri, about 1700 on March 7.
This
was followed by a Malfunctioning and Defects Report, dated March 9, t o the
l o c a l FAA office.
On March 3, f r o m t h e examination of t h e Allegheny pro-
peller, Allison personnel were aware of t h e two Improperly heat t r e a t e d
- 21 torque pistons which had caused a readily detectable malfunction.
However,
a t t h i s time they did not consider the condition an unairworthy one o r an
hminent hazard t o f l i g h t .
When there was s u f f i c i e c t i r z o m a t i o n available
from t h e Lake Central accident investigation, t h i s , together with t h e
Allegheny propeller information, prompted t h e telephone c a l l of March 7 in
"which Allison recommended, physical examination of the suspect propellers.
The next day t h e Airworthiness Directive requiring t h i s action was issued by
the FAA.
The FAA Engineering D i s t r i c t o f f i c e f i r s t learned of t h e torque
piston problem on March 8, when it saw the AD.
The Allison Division of
General Motors holds, among others, Production C e r t i f i c a t e s f o r the manuf a c t u r e of engines and propellers used on t h e Prop-Jet Convair and other
aircraft.
FAR Part 21.139 s t a t e s t h a t an applicant f o r a Production C e r t i f i -
c a t e must show t h a t he has established and can maintain a q u a l i t y control
systea so t h a t each product w i l l meet the design provision of the c e r t i f i c a t e .
FAR Part 21.165 makes it t h e responsibility of t h e manufacturer f o r determining
t h a t each completed product i s i n a condition f o r safe operation.
I n practice, before a Production C e r t i f i c a t e is issued, t h e FAA reviews
an applicant's q u a l i t y control plan and inspects h i s f a c i l i t y t o determine
i f the plan and f a c i l i t y meet t h e regulatory requirements.
After the
issuance of a Production C e r t i f i c a t e , FAA Manufacturing Inspectors maintain
general surveillance over t h e operations and f a c i l i t i e s of a c e r t i f i c a t e
holder f o r continued adherence t o t h e regulatory requirements.
The FAA
Engineering and Manufacturing D i s t r i c t o f f i c e i s responsible f o r manufacturing
surveillance under Production and Repair Station Certificates, p a r t i c i pation in Inspections f o r type c e r t i f i c a t e s and. t h e work associated with
t h e issuance of Airworthiness C e r t i f i c a t e s f o r o r i g i n a l a i r c r a f t .
For t h i s
work the o f f i c e is s t a f f e d with three Manufacturing Inspectors, and i t s area
of responsibility includes Indiana and p a r t s of two other states.
35 manufacturers i n i t s area.
There were
Allison i s the l a r g e s t but some of the others
have several hundred employees.
In practice, manufacturing surveillance is accomplished by dividing
t h e production and q u a l i t y control areas i n t o nanufacturing control areas
and inspecting i n each area f o r compliance with the approved production
specification data.
I n t h e case of Allison there a r e 51 such control areas
with respect t o engines and propellers, 22 of which were s t r i c t l y propeller
areas.
year.
The FAA office i s required t o inspect each area a t l e a s t once each
About 150-man hours per year a r e spent i n the Allison plants.
Inspectors from t h e Engineering and Manufacturing D i s t r i c t o f f i c e made
regular and frequent v i s i t s t o Allison i n connection with t h e i r various
functions.
The records r e f l e c t t h a t a number of reccenmendations were made
by t h e inspectors over a two-year period preceding the Lake Central accident,
but none was d i r e c t l y r e l a t e d t o production and q u a l i t y control changes made
by Allison based on t h e torque piston experience.
1.13
There was no f i r e involved i n t h e accident.
1.14
Survival Aspects
The accident was nonsurvivable.
- 23 1.15
Tests and Research
The Allison Chief Project Engineer f o r the 6064. propeller reported
t h a t when t h e s p l i n e s of t h e torque piston were s u f f i c i e n t l y worn away,
t h e piston would move a s a f r e e piston t o t h e outer l i m i t of the torque
cylinder.
He s t a t e d t h a t calculations showed t h a t a s a r e s u l t of t h i s
movement, a c e r t a i n amount of imbalance would be created and t h e operating
o i l pressure would increase about 33 percent.
The piston, having moved t o
and retained by t h e cylinder end cap,would increase t h e cylinder wall load.
from about 2,400 pounds t o about &,OW pounds with a r e s u l t a n t increase i n
s t r e s s up t o 99,000 p.s.i.
A t e s t was run t o determine t h e f a t i g u e strength of t h e torque cylinder.
I n t h e t e s t a cyclic load of 1100 t o 2800 p.s.i.
was used t o simulate t h e
operating pressure load of a torque cylinder with a f a i l e d piston.
cylinders were tested.
67,000 cycles.
Two
The f i r s t f a i l e d a t 62,ltoo cycles and t h e other a t
These r e s u l t s indicated a torque cylinder could operate with
a f a i l e d piston up t o about 500 hours before it f a i l e d .
The t e s t f a i l u r e s
and t h e f a i l u r e from the accident a i r c r a f t were similar.
Another t e s t was made t o determine t h e approximate r a t e of propeller
pitch decrease which would occur i f t h e r e were a sudden and t o t a l l o s s of
o i l pressure on the torque piston.
A d i e s e l r i g driving a propeller instru-
mented t o measure p i t c h r a t e change of t h e blades was used, with a provision
t o simulate a sudden l o s s of o i l pressure under operating conditions.
Tne
t e s t indicated t h e blades would pitch down a t a r a t e of about 130 degrees
per second.
- 24 With t h e above test information, d i g i t a l computer program studies
were run t o r e l a t e the f a i l u r e t o t h e f l i g h t conditions of Flight 527 and
t o determine t h e dynamic effect on propeller r.p.m.,
and propeller blade s t r u c t u r a l strength.
p i t c h lock reaction
The r e s u l t s shoved t h a t it would
take the propeller 0.10 second t o increase t o 1055 r.p.m.,
the pitch lock
engage speed., and 0.084 second f o r t h e pitch lock t o respond and lock the
blade angle.
In t h i s t i n e , however, t h e blade angle would have decreased
from 49 degrees t o 28 degrees.
At 28 degrees t h e propeller r.p.m.
l l 4 percent of nonual operating r.p.m.
crease t o 196 percent.
but the r.p.m.
would be
would continue t o in-
At 1.80 percent the design strength of the propeller
blades would be exceeded.
During design and development of t h e propeller, t h e pitch lock was
t e s t e d t o a blade angle change r a t e of 40 degrees per second.
This was con-
sidered t h e maximum r a t e which could r e s u l t from any single primary f a i l u r e ,
which vas t h e f a i l u r e design c r i t e r i o n f o r t h e propeller.
2.
2.1
ANALYSIS AND CONCLUSIONS
Analysis
Based on the evidence obtained during the investigation and Public
Hearing i n connection with t h i s accident t h e Safety Board concludes t h a t
t h e crew of Flight 527 were well qualified and t h a t preparations f o r the
f l i g h t were made i n a routine manner.
The f l i g h t progressed v l t h no d i f f i -
c u l t y and a t 2006 was over t h e v i c i n i t y of Marseilles, Ohio, descending i n
instrument weather conditions a t 8,000 f e e t on a magnetic heading of 322
degrees, with an indicated airspeed of 254 knots.
At t h i s time, with no
- 25 warning t o t h e crew t h e r i g h t propeller oversped and i t s blades separated.
The No. 2 blade penetrated t h e a i r c r a f t fuselage, destroying its s t r u c t u r a l
i n t e g r i t y t o t h e extent t h a t , coupled with t h e force of v i o l e n t r i g h t yaw
created by t h e propeller separation, t h e fuselage f a i l e d causing t h e a i r c r a f t t o crash.
The Board concludes t h a t no malfunction o r f a i l u r e other than t h a t
associated with t h e r i g h t propeller was causative i n t h e accident.
Clear physical evidence, hereinbefore described, shows that t h e No. 2
propeller blade penetrated t h e lover r i g h t s i d e of t h e a i r c r a f t fuselage i n
l i n e with t h e propeller plane.
An analysis of t h e danage, i t s nature and
locations, shows t h e blade pierced t h e structure, t i p end f i r s t , while moving
on a tangent t o t h e propeller arc and r o t a t i n g clockwise end over end.
Due
t o the rotation, a f t e r t h e i n i t i a l penetration t h e blade had r o t a t e d enough
t h a t i t s t i p end cut through t h e upper right side of t h e fuselage from inside t o outside.
The r o t a t i n g blade then continued through t h e i n t e r i o r of
t h e fuselage on an upvard s l a n t and penetrated t h e upper l e f t side of the
fuselage, butt-end f i r s t , from inside t o outside.
The c u t t i n g and breaking
of the penetrations destroyed about 50 percent of t h e s t r u c t u r a l i n t e g r i t y of
t h e fuselage.
The l o s s of i n t e g r i t y under t h e force of a violent r i g h t yaw
created by t h e propeller separation caused the fuselage t o separate along
the l i n e s of penetrations.
The a i r c r a f t then f e l l with t h e two sections of
fuselage .joined only by the control cables and one e l e c t r i c a l wiring bundle.
Metallurgical examination revealed t h a t t h e h e l i c a l splines of t h e No. 3
torque piston of t h e r i g h t propeller were worn away because the part had not
- 26 been nitrided f o r surface hardening during manufacture.
The torque cylinder
had f a i l e d i n fatigue with a sudden and t o t a l separation.
This infomation,
together with functional and t e s t data on t h e propeller, provided the basis
from which an analysis of t h e sequence of f a i l u r e events was reconstructed.
I n the sequence, when t h e torque piston splines were s u f f i c i e n t l y vorn,
probably several hundred hours before t h e f a i l u r e of the cylinder, the piston
moved a s a f r e e piston t o t h e outer l i m i t of t h e cylinder.
Stress loads were
thereby imposed a t the junction of the piston and splined area i n t h e order
of 88,000 p.s.i.,
which exceeded the design f i n i t e f a t i g u e l i f e of the part.
Unfortunately, the cylinder f a i l u r e was a sudden and t o t a l separation, a s
compared t o t h e more c h a r a c t e r i s t i c fatigue f a i l u r e of a gradual breakthrough
of t h e cylinder w a l l which could well have resulted In a detectable warning
o i l leak before t o t a l separation.
When the cylinder f a i l e d i n t h e manner it did, there was an immediate
and t o t a l l o s s of o i l pressure controlling the propeller blade pitch a t about
49 degrees f o r the existing f l i g h t conditions of t h e a i r c r a f t .
Under t h e
aerodynamic twisting moments the blades moved toward low p i t c h a t an e s t i mated r a t e of 130 degrees per second.
The propeller p i t c h lock was unable
t o a r r e s t t h e p i t c h change before the blades reached t h e low pitch stop and
oversped, causing t h e blades t o f a i l i n overstress.
A s nearly a s can be
determined, t h e time element between t h e cylinder f a i l u r e and propeller blade
separation was a matter of 1 t o 2 seconds.
While it i s d e f i n i t e t h a t t h e torque piston from t h e Lake Central a i r c r a f t along with 9 others missed the n i t r i d i n g process during manufacture,
- 27 t h e evidence i s i n s u f f i c i e n t f o r t h e Board t o determine with s p e c i f i c i t y
how t h e omission occzirred and how it escaped detection.
The Board i s of
t h e opinion, however, t h a t both were d i r e c t l y associated with the movement
of 10 torque pistons from the production flow t o t h e laboratory and back
i n t o t h e production system.
It i s inconceivable t o the Board t h a t t h i s was
not involved when 10 torque pistons were taken t o t h e laboratory, given distinguishing marks and t h e r e a f t e r 10 torque pistons so marked were found defective.
Because the p a r t s missed the n i t r i d i n g process it i s not d i f f i c u l t
t o understand t h a t they missed the case and core hardness check, since t h i s
was an i n t e g r a l step i n t h e n i t r i d i n g process.
It i s much more d i f f i c u l t
t o deduce how t h e n i t n d i n g omission was not detected a t f i n a l inspection.
While t h e Board i s aware of possible explanations it finds t h a t none i s
adequately supported o r compatible with t h e available evidence t o t h e exclusion of another.
When the defective torque pistons were manufactured between February
and June, 1966, Allison had an established q u a l i t y control system.
It
u t i l i z e d f u l l time personnel furnished with s u i t a b l e working conditions,
t o o l s and equipment t o perform t h e i r duties and t h e personnel were qualified
and given s a t i s f a c t o r y instructions.
The system provided redundancy t o
assure the r e q u i s i t e q u a l i t y of p a r t s i n t h a t ( 1 ) r e s p o n s i b i l i t y was placed
on each manufacturing u n i t t o perform according t o specifications n t h
q u a l i t y mspection checks m t h e form of sampling a w i n g the manufacturing
process and (2) a 100 percent f i n a l inspection vas u t i l i z e d a s a backup
check a t t h e completion of t h e manufacturing process.
These q u a l i t y control
- 28 provisions could be expected t o assure the r e q u i s i t e quality of p a r t s
and t o s a t i s f y t h e requirement of a s a t i s f a c t o r y q u a l i t y control system.
In addition, the system, a s w e l l as the f a c i l i t i e s , were inspected and
deemed s a t i s f a c t o r y by FAA leans i n connection with the issuance of production c e r t i f i c a t e s on two occasions, f i r s t i n 1956 when production of
the 501-D13D engines and A64.41 FM-606~propellers was s t a r t e d and again,
a s required when the Allison f a c i l i t i e s were moved from Vandalia, Ohio, t o
Indianapolis, Indiana, i n 1960.
During t h i s period t h e system did, i n f a c t ,
produce torque pistons of r e q u i s i t e q u a l i t y f o r the 606A propeller.
It m u l d have been d i f f i c u l t t o a n t i c i p a t e t h a t personnel breakdowns
could occur in such a way t h a t t h e previously mentioned elements of redundancy i n t h e q u a l i t y control system would be circunvented a s i n t h i s
instance.
With the benefit of hindsight, however, it can be seen t h a t
procedures i n the q u a l i t y control system should have provided f o r a s t r i c t e r
accountability of p a r t s i n t h e production processes and p a r t i c u l a r l y under
circumstances wherein the no&
production flow was interrupted and p a r t s
were handled f o r special purposes out of t h e normal sequence.
This i s
evident i n t h a t t h e 10 torque pistons missed major steps i n the n i t r i d i n g
process and t h e omission went undetected.
The evidence shows t h a t t h e FAA has a res-ponsibility t o conduct surveillance over t h e manufacturing operations of Allison, t o check f o r
continued adherence t o the regulatory requirements of the manufacturer's
'
Production Certificate, and t o check i t s products a t various production
areas f o r conformity t o design specifications.
5/
The surveillance
Sections 601, 603, and 605 of the Federal Aviation Act of 1958,
a s amended (49USC 1421, 1423, 1425).
responsibility, however, has been interpreted by t h e FAA a s not requiring
a d e t a i l e d q u a l i t y c o n t r o l surveillance program, o r a sharing in t h e manu-
'
f a c t u r e r ' s r e s p o n s i b i l i t y f o r determining t h a t each completed product i s
i n a condition f o r safe operation.
The Board believes t h a t while it was
possible f o r t h e FAA Manufacturing Inspectors t o have detected t h e weakness
i n Allison's q u a l i t y control system, as a p r a c t i c a l matter, it i s unlikely
under t h e existing procedures, t h a t t h e surveillance would have detected a
weakness "which was not apparent t o f u l l time, responsible Allison personnel
and which weakness involved personnel errors i n t h e execution of t h e system
rather than a deficiency i n t h e system i t s e l f .
A s a f i n a l consideration t h e Board believes that t h e special o i l check
was performed by Lake Central maintenance personnel i n accordance with t h e
i n t e n t of the Allison instruction, but t h e check f a i l e d t o serve i t s intended purpose.
There i s no s a t i s f a c t o r y explanation f o r the f a i l u r e because
general and past experience would indicate an o i l check t o be a s u i t a b l e
method f o r detecting metal contamination.
Without intending t o r e l y on
events a f t e r t h e f a c t , the Board does believe t h a t t h e effectiveness of the
o i l check could have been evaluated more thoroughly before it was Used.
The
f a c t t h a t Allison did not consider t h e defective torque piston an u n a i m r t h y
condition and did not notify t h e FAA, indicates t o t h e Board t h a t the seriousness of t h e o v e r a l l problem was underestimated.
6/
Section 21.139 of the Federal Aviation Regulations (14 CER 21.139).
- 30 2.2
Conclusions
( a ) Findings
1. The crew of Flight 527 were properly c e r t i f i c a t e d and
qualified f o r the f l i g h t .
2.
The aircraft was properly c e r t i f i c a t e d and maintained but
at t h e i n i t i a t i o n of Flight 527 it
TOS
unairworthy due t o
a defective torque piston i n the right propeller.
3.
Flight preparation was routine and t h e f l i g h t progressed
v l t h no apparent d i f f i c u l t y u n t i l it was near Marseilles,
Ohio, a t 2006.
4.
Loads on the torque cylinder caused by t h e failed, torque
piston of t h e No. 3 blade of t h e r i g h t propeller exceeded
t h e f i n i t e f a t i g u e l i f e of t h e cylinder and it f a i l e d In
fatigue.
5.
The l o s s of o i l pressure i n t h e r i g h t propeller due t o t h e
failed, torque cylinder caused t h e propeller pitch t o decrease
a t a r a t e ¥whicexceeded t h e propeller pitch lock capability.
6. The r i g h t propeller oversped, causing t h e blades t o separate
i n overstress.
7.
The No. 2 propeller blade of t h e r i g h t propeller
penetrated the fuselage, destroying t h e s t r u c t u r a l
i n t e g r i t y t o the extent t h a t together with the f o r c e of
a r i g h t yaw attending t h e propeller separation, t h e
fuselage f a i l e d along t h e l i n e of the propeller penetrations.
8.
The torque piston of t h e No.
3 blade had. not been n i t r i d e d
f o r surface hardening of the h e l i c a l splines during manufacture.
9. The omission of t h e n i t r i d i n g process was not detected by
inspection.
10.
The omission of the n i t r i d i n g process -was associated with
t h e movement of 10 torque pistons from t h e normal production
flow t o the Allison laboratory and return t o the production
process.
11. The Allison q u a l i t y control system lacked t h e accountability
necessary t o assure t h e r e q u i s i t e q u a l i t y of t h e individual
parts.
12.
The metal contamination o i l check t o i s o l a t e defective
torque pistonsdid not serve t h e intended purpose.
13. Allison underestimated the seriousness of t h e defective
torque piston problem.
- 32 (b)
Probable Cause
The Safety Board determines t h a t t h e probable cause of t h i s
accident
TOS
t h e f a i l u r e of the r i g h t propeller due t o omission of t h e
torque piston n i t r i d i n g process during manufacture,
and, t h e
f a i l u r e of
manufacturing q u a l i t y control t o detect the omission.
BY THE 1IATIONAL TBA1ISPORTATION SWETY BOABB:
OSCAR M. LATOEL
Member
JOHN H. REED
Ifember
LOOIS M. T
H
A
m
Member
FRANCIS H. McADAMS
Member
Joseph J O'connell, Jr., Chairman, did not take part i n the adoption
of t h i s report.
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