The
following information has been determined from preliminary readout and
analysis of flight 361’s flight recorders. Flight 361 was equipped
with both a COCKPIT VOICE RECORDER and a FLIGHT DATA RECORDER. Both
recorders were replayed at the Accident Investigation Bureau’s recently
acquired flight recorder laboratory located in Abuja. International
flight recorder experts from Canada who designed the laboratory assisted
the investigation team with the readout and analysis process along with
representatives from the aircraft manufacturer and aircraft operator,
Associated Airlines. We are conducting the investigation in accordance
with the provisions of International Civil Aviation Organization (ICAO)
Annex 13, of which Nigeria is a member State.The flight data recorder or
FDR contained approximately 47 hours of data in solid state memory.
The recorder downloaded without issue.
There were approximately 50 parameters
recorded. A few parameters were not working properly however we do not
think, in this particular case, that it will hamper the overall
investigation.The cockpit voice recorder or CVR was an older generation
magnetic tape based device. The CVR’s magnetic tape recording was
removed from the unit and replayed on an open reel 4 track tape deck
specially adapted for replaying CVR’s of this type. The CVR contained
32 and one half minutes of audio which included the internal
conversation of the two pilots, radio calls and the overall aural
environment in the cockpit on the cockpit area microphone. The CVR was
of good quality and the team is in the process of generating a complete
transcript of all relevant information.
The AIB plans to release the transcript
as part of its final report of the accident however the actual recording
is, under international protocol, sensitive and therefore privileged
information and will not be released at any time.The following
represents information that has been determined from our preliminary
assessment of both flight recorders:The crew discussed some concerns
about the aircraft prior to departure but at this time we are not
prepared to elaborate on those concerns as there remains a lot of work
to complete on the CVR analysis in order to determine the specific
nature of the crew’s concerns. Associated 361 was cleared for take-off
on runway one eight left at Lagos international airport. The wind was
calm and weather is not considered a factor in this accident.
Approximately 4 seconds after engine power was advanced to commence the
take-off roll, the crew received an automated warning from the onboard
computer voice which consisted of three chimes followed by
“Take-off Flaps…Take-off Flaps”. This
is a configuration warning that suggests that the flaps were not in the
correct position for take-off and there is some evidence that the crew
may have chosen not to use flaps for the take-off. The warning did not
appear to come as any surprise to the crew and they continued normally
with the take-off. This warning continues throughout the take-off
roll. As we are in the process of verifying the accuracy of the flight
data, we have not yet been able to confirm the actual flap setting
however we expect to determine this in the fullness of time.It was
determined from the CVR that the pilot flying was the Captain and the
pilot monitoring and assisting was the First Officer.The ‘set power‘
call was made by the Captain and the ‘power is set’ call was confirmed
by the First Officer as expected in normal operations. Approximately 3
seconds after the ‘power is set’ call, the First Officer noted that the
aircraft was moving slowly.
Approximately 7 seconds after the ‘power
is set’ call, the internal Aircraft Voice warning system could be heard
stating ‘Take off Flaps, Auto Feather’. Auto feather refers to the
pitch of the propeller blades. In the feather position, the propeller
does not produce any thrust. The FDR contains several engine related
parameters which the AIB is studying. At this time, we can state that
the Right engine appears to be producing considerably less thrust than
the Left engine. The left engine appeared to be working normally. The
aircraft automated voice continued to repeat ‘Take-off Flaps, Auto
Feather’.
The physical examination of the wreckage
revealed that the right engine propeller was in the feather position
and the engine fire handle was pulled/activated.The standard ‘eighty
knots’ call was made by the First Officer. The first evidence that the
crew indicated that there was a problem with the take-off roll was
immediately following the ‘eighty knots’ call. The First Officer asked
if the take-off should be aborted approximately 12 seconds after the
‘eighty knots’ callout. Our investigation team estimates the airspeed
to be approximately 95 knots. Airspeed was one of the parameters that,
while working in the cockpit, appeared not to be working on the Flight
Data Recorder. We were able to estimate the speed based on the radar
data that we synchronized to the FDR and CVR but it is very approximate
because of this.
In response to the First Officer’s
question to abort, the Captain indicated that they should continue and
they continued the take-off roll. The crew did not make a ‘V1’ call or a
Vr’ call. V1 is the speed at which a decision to abort or continue a
take-off is made. Vr is the speed at which it is planned to rotate the
aircraft. Normally the non-flying pilot calls both the V1 and the Vr
speeds. When Vr is called the flying pilot pulls back on the control
column and the aircraft is rotated (pitched up) to climb away from the
runway. During the rotation, the First Officer stated ‘gently’, which
we believe reflects concern that the aircraft is not performing normally
and therefore needs to be rotated very gently so as not to
aerodynamically stall the aircraft.The First Officer indicated that the
aircraft was not climbing and advised the Captain who was flying not to
stall the aircraft. Higher climb angles can cause an aerodynamic
stall. If the aircraft is not producing enough overall thrust, it is
difficult or impossible to climb without the risk of an aerodynamic
stall.
Immediately after lift-off, the aircraft
slowly veered off the runway heading to the right and was not climbing
properly. This aircraft behavior appears to have resulted in the Air
Traffic Controller asking Flight 361 if operation was normal. Flight
361 never responded.
Less than 10 seconds after rotation of
the aircraft to climb away from the runway, the stall warning sounded in
the cockpit and continued to the end of the recording. The flight data
shows characteristics consistent with an aerodynamic stall. 31 seconds
after the stall warning was heard, the aircraft impacted the ground in a
nose down near 90 degree right bank. The investigation is focussing on
the following:1) Mechanical and electronic engine control issues
related to the Right engine and Right engine propeller systems.2)
Aural warnings related to auto-feather and the flap settings required
for takeoff.3) Take-off configuration issues with respect to flap
settings.4) Crew decision making and training with respect to
proceeding with the flight despite concerns regarding the aircraft’s
suitability for flight.5).
When and how the number 2 engine fire
handle was pulled.6) Standard operating procedures with respect to
continuing the take-off roll despite continuous automated voice warnings
of both ‘take-off flaps’ and ‘auto feather’ when there was ample time
to abort the take-off.7) The airline management’s safety culture
fostered throughout the airline.We are in the process of developing a
comprehensive computer reconstruction of the flight which will help our
team understand the sequence of events and will ultimately help us
communicate our findings to the aviation community and the general
public. At this time we have no urgent safety recommendations. We will
not wait for the final report to issue safety recommendations should any
issue arise that we feel needs immediate attention.
Capt. Muktar Usman, Commissioner, Accident Investigation, Prevention Bureau (AIPB)11/10/13
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