Tuesday, December 27, 2016

Jet Airways 9W2374 Goa Dabolim Airport Runway 26 Excursion

Jet Airways flight 9W2374 departed off of the side of VOGO Goa Dabolim runway 26 (mag heading 261) shortly after commencing their takeoff roll.

Boeing 737-85R
Registration VT-JBG
Manufacturer Serial Number 35083

Date and Time of incident:
262333Z  or Dec 27, 5:03am local

Winds were calm, with visibility reduced to 3000m in mist and haze, and no significant clouds.

Sunrise was about 7am local, skies were dark at the time.

Runway 26 is 11253 x 150 feet / 3430 x 46 meters 

Coordinates: N15°23.05' / E73°51.13'
Elevation: 183 feet
Runway Heading: 261°

From flightradar24.com data.

9W2374 taxi to the runway 26 threshold, made a 180 degree turn and lined up with runway 26.

After about a minute from lining up, 9W2374 began their takeoff roll.

First ADS-B report shows track heading of 258 and speed 26 kts.

2nd ADS-B report: 6 seconds later the airplane track has shifted to the right 10 degrees, the 9W2374 has accelerated to 35 its and appears to be departing the runway.

3rd ADS-B report:  9W2374  continues accelerating to 49 kts off the runway.

4th ADS-B report: 9W2374 takes a right turn and begins to slow, down to 37 kts (about 12 seconds after leaving the runway).

5th ADS-B report: 9W2374 continues to turn to the right and continues to slowly decelerate, now down to 31 knots almost 18 seconds after leaving the runway, and stops shortly thereafter.

It appears 9W2374 lost directional control at the beginning of their takeoff roll.  Winds were negligible, not representing a cross-wind threat.  Visibility was reduced, but adequate for the takeoff. It was dark.

Peak speed was achieved about 12-15 seconds after commencing the takeoff, at 49 knots, well off of the runway surface.

With the loss of control apparently below 40 knots, it does not seem likely that a rudder malfunction would have had sufficient authority to drive the airplane off-course.

Generally, pilots will advance engines to an intermediate power setting prior to setting takeoff power.  This spool up from low idle ensure that both engines will advance to takeoff power in concert, making asymmetric thrust less likely.

Unofficial Boeing 737 FCOM

Without engine readings, it is not possible to know if asymmetric thrust led to loss of control.

Initial reports show a possibility that the right engine thrust reverser may be deployed, the left appears to be stowed.  The airplane would would be driven to the right with takeoff power set and the right engine toggling to reverse thrust. (thanks to pprune.org user daelight).

Nose wheel steering, brakes, and tires/wheels could each have created an excursion off of desired heading.  

It is curious that 9W2374 continued to accelerate even after leaving the runway surface.  Normally power would be rapidly retarded to idle in this scenario, but in this case, power appears to not have been retarded for some time (5-10 seconds) after directional control was lost.

Uncommanded thrust reverser is prevented by design incorporating a sequence of features that offer independent barriers.  The Lauda 767 catastrophe brought awareness of unexpected upper wing airflow disturbance if encountered in cruise (FAA lessons learned), which led to rapid loss of control and inflight breakup. Boeing would have accounted for these concerns not just because of the Lauda accident, but by further examinations of the preceding CFM56-3 reverser which needed additional features by airworthiness directive as a result of the scrutiny AD 94–21–05 R1.

Stay tuned!

Peter Lemme
peter @ satcom.guru

Follow me on twitter: @Satcom_Guru

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Peter Lemme has been a leader in avionics engineering for 35 years. He offers independent consulting services largely focused on avionics and L, Ku, and Ka band satellite communications to aircraft. Peter chairs the SAE-ITC AEEC Ku/Ka-band satcom subcommittee developing PP848, ARINC 791, and PP792 standards and characteristics. 

Peter was Boeing avionics supervisor for 767 and 747-400 data link recording, data link reporting, and satellite communications. He was an FAA designated engineering representative (DER) for ACARS, satellite communications, DFDAU, DFDR, ACMS and printers. Peter was lead engineer for Thrust Management System (757, 767, 747-400), also supervisor for satellite communications for 777, and was manager of terminal-area projects (GLS, MLS, enhanced vision).

An instrument-rated private pilot, single engine land and sea, Peter has enjoyed perspectives from both operating and designing airplanes.  Hundreds of hours of flight test analysis and thousands of hours in simulators have given him an appreciation for the many aspects that drive aviation; whether tandem complexity, policy, human, or technical; and the difficulties and challenges to achieving success.

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