There has been a lot of non-professional press coverage on the incident involving Jet Airways flight departing Goa on 27 Dec 2016. It was reported that the aircraft skidded off the runway while aligning for the take-off and elsewhere, it was reported that it was due to engine failure. There was more to the incident than what was reported.
The technical report from the DGCA (PIB) will present the facts of the case and reasons of the mishap. In the matters of flight safety, it is of utmost importance to understand the cause of accident and draw lessons from it so that in future such mishaps are avoided. The aim of any accident investigation cannot be to apportion the blame or malign the pilot or the operator but improve safety.
Factors contributing to the the aircraft’s veering off must be brought out in public both in the interest of flight safety and to professionally clear the ambiguity surrounding the incident with explanation at each stage to the larger audience, which is ever hungry for right information. The analysis below is based upon the information available in public domain and my own experience as a pilot.
SEQUENCE OF EVENTS AS IT HAPPENED ON JET AIRWAYS FLIGHT 9W 2374
- Pilot engages Take-Off / Go Around switch to commence the take-off run. TO/GA switch signals both engines through computers to increase fuel flow to generate 54000 lbs of Engine Thrust to be developed in 4-7 seconds.
- In response to increase in power, the air speed comes alive and aircraft accelerates. Aircraft speedometer registers speed above 30 knots or 54 kmph. Air speed is crucial to maintain the direction by rudders. At lower speeds, rudders are ineffective and they become more and more effective as speed increases. The direction control of aircraft at low speeds is primarily maintained by nose wheel steering through rudder pedals which can control direction in the forward direction with 10 degrees of variance either side from the longitudinal axis.
- It appears that it is during the engine acceleration at (N1) 74% rpm, that the malfunction happened.
- The right reverser got engaged. (As per information available in public domain)
The right engine that was producing forward thrust of say 20,000 lbs suddenly started to produce reverse thrust of 20,000 lbs while the left engine was producing forward thrust of 27,000 lbs.
This malfunction could only happen because of simultaneous multiple failures which is even rarer than a simple engine failure.
It is worse than having an engine failure because a failed engine produces almost zero thrust and hence, simply slows down the acceleration with small change in the direction as the operative engine is offset from the central axis of the aircraft. All aircraft are certified to be safe to remain on the runway either during take-off or landing or at any time during flight following simple engine failure. However, deployment of reverse thrust at any stage of flight is neither guaranteed nor certificated to be a situation which is fully controllable. Hence, multiple electronic and mechanical locks and latches are placed to prevent an unintentional Reverse Thrust Deployment.
A Reverse Thrust Deployment at low speed on ground is much more difficult than simple engine failure during take-off roll. The brute force of total 54,000 pounds (27000Kgf) which catapults the aircraft weighing 70 tons and launches it into the air, is now engaged in spinning the aircraft. In this case, to the right. The figure below will be appropriate to understand the gravity of the problem.
For a pilot to react to this situation within human limitation to see, analyse and react on the take-off segment, he/she is allowed just two seconds. A reaction time less than this is humanly impossible and all emergencies as a pilot is designed with this premise.
There are three factors that delays even the most instantaneous reaction by the pilot after the recognition of the problem:
- The only direction control available to the pilot at low speed is Nose Wheel Steering, which is ineffective unless the aircraft is moving in the forward axis. In the event of spinning, the nose wheel steering will caster and break.
- The brakes which can be applied to control the sideways movement of aircraft needs pilot to slide their feet from the floor to the brake pedal while the rudders are fully deflected. It is a task that will require reaction time of physical movement of feet. The brake that needs to be applied is left toe brake but here is the catch. As the aircraft was veering to the right, instinctively the pilot would have first applied full left rudder. Hence, his sitting posture would entail left leg fully extended and right leg bent up. In this position to lift feet and then depress left toe brakes fully is a physically challenging task, which will require time longer than 2 seconds. In this instance, the aircraft was moving at approximately 40 knots speed, which is approximately 70 foot per second on a runway which is just 75 ft width away from the centre line.
- Third and the only effective option to control the spinning of aircraft and its departure from the runway is by closing the thrust. By jet engine design, there is definite lag in production of thrust and similar time lag to reduce the thrust from full power to zero or vice versa.
From the reports available, the pilot initiated the actions as the emergent situation demanded and with promptness that a human machine is capable of at 4am in the morning. However, the machine failed to reduce the power on pilot’s command which is a situation not envisaged even by the manufacturer or operator and hence, could not be incorporated even in the training profile.
- The reverser did not disengage despite cutting throttle.
If the reverser did not disengage even after pilot’s command, the aircraft was technically doomed to depart from the runway and break as it happened and not even the best pilot in the world could have done any better. And the aircraft had already veered off the runway by then. So, what this Jet pilot did was as miraculous an act as landing the plane on water. And just how incredible is it to even contemplate the idea of landing a plane on water can be best understood by the US Airways’ plane’s crash landing in 2009 (Watch the Channel 4 documentary below)
- Fuel flow was shut to right engine and only then the right engine stopped.
Let’s be gracious and accept that the pilot did his best but a sequence of events that happened was bizzare and that damage was contained due to prompt action in a situation for which he was probably not even adequately trained or a failure not envisaged. Aviation training syllabus will probably include more of such exercises in future. It is easier to criticise in the comfort of air conditioned drawing rooms than to go out and bat in the chilling night when the chips are down.
(The author is a former Air Force officer and currently a professional pilot)