Air Crash Investigation: Flight 191

Topics: Air safety, National Transportation Safety Board, McDonnell Douglas DC-10 Pages: 8 (1114 words) Published: December 11, 2012


Air Travel
Most effective and safest forms of transport
< 1 for every 2 x 109 personmiles flown

Air crash – One of worst situation
Team Members: Seran Karikalan 1002764 Sivaguru S/O Sivagnanam 1003260 Ng Aiting 1067138 DARE 3B 24

Number of lives it takes with it

Human Error
Manufacturers to Engineers
No one wishes for air crashes

On 25th May 1979, 15:00Hrs
A McDonnell Douglas (MD) DC-10 American Airlines Took-off from Chicago O’Hare Int. airport

Yet, 70% is caused by Human errors “That wouldn’t happen to me” Is main cause for such errors

Just before lift off
Lost power from No.1 engine

Suddenly rolled heavily to left
Smoke gushing out

Air crash do not occur independently Led by ‘chain of errors’ Any one broken link would prevent it

Within 30 seconds
Smashed into nearby trailer park

Series of events Maintenance factors Other contributing factors Error preventing strategies

All on-board 271 + 2 other dead



Crash Involved…
On 25th May 1979, American Airlines Flight 191 was en route from Chicago, O’Hare airport to Los Angles, California Had carried 258 passengers and 13 crew members on board



8 weeks before the crash Flight 191
– Major Maintenance – Spherical Bearings had to

On Crash Day…
– During Take off the left engine

be replaced
– Engine and pylon had to

be removed to gain access
– Came up with own

– Crack formed in hidden

and pylon ripped off from the left wing – Damaged a meter of leading edge, hydraulic system – Electrical power was disabled as left engine generated electricity



On Crash Day…
– The loss of hydraulic power

caused Slats to retract due to ram air effect – Stick shaker had failed due to electrical power loss – Plane had loss of lift on the left wing – Plane stalled, rolled left and crashed



Maintenance Error
MD issued 2 Service Bulletins
Change of spherical bearing 2 years prior to accident

Change of Procedure
The stated procedure
Remove engine first Remove pylon Replace the bearings

Only in March ‘79
American Airlines carried out replacement

Engineers felt it troublesome
Came up with own procedure

Change of Procedure
Removing engine & pylon
As a single unit

Change of Procedure
Although MD discouraged them
Do not have authority to prevent them

Continental & United Airlines did it before Lesser man hours required Lesser disconnects can be achieved ○ 79 to 27

After evaluation
Used industrial forklift to raise/lower the engine Instead of an engine cradle

Change of Procedure
Removal of bolts
From thrust link assembly was altered Last few bolts were difficult to remove

Error Sequence
Used forklift
Inadequate as its not stable It was faulty

Reversed the order of removal
When the engine was not removed Put large stress on flange
○ Flange – metal piece

Incorrect order of bolt removal
Put large stress on flange

secures rear side of engine to wing

Changed shift at crucial moment



Error Sequence
During lifted up position
Forklift was moved to properly align it Caused engine/pylon to rock about Crack initiated on flange

Crack was in hidden area
It escaped from view

Aircraft returned to service
Without eliminating latent failure

Deficiencies in Communication
Poor communication between maintenance crew, airline management and FAA Alternation to the maintenance procedure Damaged flange not reported to FAA Sequence of removing bolts altered

Organizational Culture
Major & minor errors during maintenance not reported
• Usage of forklift not informed

Company policy not followed properly
• 3 crew signing on a job card • Hard to track down person doing the


Alternation to procedure become a norm

Impropriate Take-off Procedure
No.1 engine flew off when...
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