Jet 737 aborts takeoff, leaves runway - Goa [Archive]

Sqwak7700

27th Dec 2016, 12:54

Sounds like pressing TOGA with an asymmetric engine speed, most likely caused by having one engine at a higher setting during the 180 degree turn at the node.

If #1 thrust had been used to help turn the aircraft while #2 stayed at idle, and then TOGA was pressed before allowing both engines to stabilise, you could easily lose control. #1 would accelerate much quicker to TO thrust, while #2 would have to accelerate from idle.

Never flown the 73, but I've ridden the jumpiest many times before. Those CFMs have a very long spool up time from idle. If the pilot was distracted or didn't get on top of it quickly enough, things can very quickly turn pear-shaped.

Goat Whisperer

27th Dec 2016, 13:08

Squawk7700

that scenario happened to a 738 at a company related to mine. Departed the intended runway but luckily ended up on the crossing strip. Highly likely in this scenario, imo.

lomapaseo

27th Dec 2016, 14:35

In this day and age uncommanded reverser deployment would be very unlikely

I believe that you can command a single reverser to deploy when on the ground. But why in this case would be the next question.

sansmoteur

27th Dec 2016, 14:51

Sqwak7700

Plausible

AtomKraft

27th Dec 2016, 15:03

If you get, for whatever reason, a big thrust asymmetry at LOW speed, this is the likely result.

ie you are below VMCG and VMCA.

What's going to keep it straight? Not rudder certainly.

Sure, pulling both to idle will save the day- but if you weren't trained for, or expecting it, a low speed asymmetric yaw will ceretainly punt you off the runway.

Of course, most engine failures happen just as one passes V1....:rolleyes:

Airbubba

27th Dec 2016, 15:05

I plotted the FR24 ADS-B data.

Satcom Guru: Jet Airways 9W2374 Goa Dabolim Airport Runway 26 Excursion (http://www.satcom.guru/2016/12/jet-airways-9w2374-goa-dabolim-airport.html)

Nice graphics and analysis as before. :ok:

From your article linked above:

Generally, pilots will advance engines to an intermediate power setting prior to releasing brakes. This spool up from low idle ensure that both engines will advance to takeoff power in concert, making asymmetric thrust less likely. Without engine readings, it is not possible to know if asymmetric thrust led to loss of control.

Actually, I think the brakes will normally be released before the initial spool up per Boeing's recommendation.

I found this, allegedly from a 737-700 FCOM:

A rolling takeoff is recommended for setting takeoff thrust. It
expedites takeoff and reduces risk of foreign object damage or
engine surge/stall due to a crosswind. The change in takeoff roll
due to the rolling takeoff procedure is negligible when compared to
a standing takeoff.

Allowing the engines to stabilize for more than approximately 2
seconds prior to advancing thrust levers to takeoff thrust may
adversely affect rolling takeoff distance.

Similar verbiage is in the manuals for the larger Boeing's I've flown.

ManaAdaSystem

27th Dec 2016, 15:09

How many of you use differential thrust to help turn a 737 ?
One engine spooling up with the other lagging behind will push the nose sideways, but you need to be really slow not to catch this.

And, you would go to the side with not much forward movement.

no sponsor

27th Dec 2016, 15:16

AtomKraft has it spot on I think. Very few are trained or expecting massive asymmetrical thrust at low speed. Governor failure could give you a similar outcome.

ManaAdaSystem

27th Dec 2016, 15:24

Are you serious?
We are all trained to recognise engine failures during takeoff at various speeds.
If you start your takeoff on one engine you will do a pirouette where you stand.
An engine seizure or a reverser deployed at "low" speed fits the scenario. If so it was handled poorly.

AtomKraft

27th Dec 2016, 16:06

You know, being trained for stuff makes a BIG difference.

For example, I've flown a RJ-85 to a dead stick landing. (in the sim) . Had the guys who ran out of fuel recently done that? I don't know, but I cocked it up badly the first time....

Ever tried an engine failure just as max thrust is reached? At low speed? Hardly the most unlikely time for an engine failure, is it?

Off you go!

Unlikely to kill anyone though....

ManaAdaSystem

27th Dec 2016, 16:24

Off you go. To the side. A few metres down the runway.
I have trained this, and I have tried it in real life. My Effoh who was in the habit of not setting 40%, but rather just push the throttles up (that is the way we used to do it on the .... fill in the blanks) did exactly that, and hit TOGA without checking anything. The left engine worked as it should, the right was not. Not an engine failure, just slow.
The nose was pushed about 2 metres to the side before I managed to close the throttles. Maybe we managed to move 10 metres down the runway.

Playing glider in the sim is a different situation to doing it in real life, in darkness and without visual contact with anything.

172_driver

27th Dec 2016, 17:12

Ever tried an engine failure just as max thrust is reached? At low speed? Hardly the most unlikely time for an engine failure, is it?

One of the first things practiced in Multi-Engine school. The swing is just as bad, i.e. uncontrollable, in a Seneca as it is in 737. Seems like modern aviators have forgotten the basics, if this happens to be the case of asymmetric spool up. As an instructor I always sat with my left hand on the mixture control < 1000 ft with new schoolers. They were good, it was just that I wanted to immediately get control of the yaw if they didn't respond properly to the failure.

lomapaseo

27th Dec 2016, 17:50

We are all trained to recognise engine failures during takeoff at various speeds.

True but

Your training presumes a lack of thrust on one engine at speed (rudder skill) and not a significant overthrust on one engine below rudder effectiveness.

And the confusion is compounded with any reversers deployed trying to figure out what end is pushing or pulling too much.

Most pilots simply end up off the side of the runway while they are deciding (data based)

AtomKraft

27th Dec 2016, 17:52

172 Driver.

No. It's not.

I've got over 12000 hours and only seen it on one of my type conversions, and that only briefly

27th Dec 2016, 18:12

Does this runway require a backtrack and 180 degree turn? How many times have I seen guys spool up the outboard engine to assist the turn (that's fine)....close the levers as they line up and then stand them up to 50% when cleared for T/O....but the spooling down engine hasn't fully idled and so it spools up faster than the other.......if you don't check for both stable at 50%.....you're going to get a big yaw. Does this runway require TOGA?

On the face of it this seems like simply not checking for BOTH stable before applying required take off thrust.

oxide

27th Dec 2016, 18:25

Yup, requires backtrack. I wouldn't imagine the 73 would need the assistance of the outboard to make the turn though. I'm from Goa and I can't remember the last time differential thrust was used to assist and can honestly say I've never had any of them go to TO thrust straight from the turn.

Having said that, this could very well be the case here.

framer

27th Dec 2016, 19:51

I think you need to reel you wild imagination in
Ok, wild imagination reeled in.
I was responding to Initial reports saying starboard engine reversor deployed during T/O roll If that happened, I stick with my original statement. I don't believe that this is what happened though. I have seen many experienced pilots depart the runway in the sim if an engine is failed at about 25 kts, and it happens in real life when one engine spools up quicker than the other. When a 737 aircraft departed runway 16R in YSSY some years ago and ended up on 07, the crew thought they had a nose wheel problem. The problem was that the right engine came up slower than the left. The nose wheel simply scrubbed along the Tarmac when NWS was used.
Like someone above said, the chances of having a reverser deployed at the start of the takeoff roll are remote.

172_driver

27th Dec 2016, 20:09

172 Driver.

No. It's not.

I've got over 12000 hours and only seen it on one of my type conversions, and that only briefly

I am not going to speak for you of course, but are you sure you never practiced the scenario in multi-engine twin prop (be it a Seneca, Duchess or Baron) all those years ago getting your Multi-Eninge rating?

I have done engine runaway during recurrent training in a 737, but guess that is something the operator has chosen to put in the program.

gearpins

27th Dec 2016, 22:46

To the B737 experts,
Can a fault induce auto deployment of the reversers while the thrust levers are out of idle posn...?

noflynomore

27th Dec 2016, 23:14

I well remember the night of V1 cut after V1 cut in the 737 sim when the instructor asked us, "got the hang of it then?" and on receiving our cocky assurances set us up one last exercise.

The beefer chopped one engine as soon as they had reached t/o N1 at perhaps 40Kts. The resulting excursion was astonishing. As was the following one. It took IMMEDIATE and EXTREME control inputs to control the swing.
By FAR the hardest EFATO drill on the 737 (and A320) is the low-speed failure with full power when no rudder authority is available to help keeping it straight. Partly because we tend to practice it less I suppose, after all, a low speed asymmetric event can't be a big deal, can it? Hell no!

The excursion of this event looks to me as if a low speed full power failure was not properly contained.

Metro man

27th Dec 2016, 23:28

Does the CFM engine have a "keep out" band like the IAE ? If the thrust levers were splayed to assist the turn and advanced towards take off thrust while still in this position, would the FADEC rapidly accelerate the leading engine through the keep out range whilst the other engine lagged behind ?

The surprise factor would be considerable but even so they still went a long way off the pavement.

tdracer

28th Dec 2016, 01:36

No keep out zone on the CFM (that's pretty much a Rolls exclusive due to fan flutter issues).
While an uncommanded reverser deployment is very remote, it is somewhat more likely on the ground than it is in flight due to the air/ground logic.

Sqwak7700

28th Dec 2016, 03:26

Squawk7700

that scenario happened to a 738 at a company related to mine. Departed the intended runway but luckily ended up on the crossing strip. Highly likely in this scenario, imo.

Same here, Goat, but on 747s. Luckily, the pilots reacted fast enough and rejected the TOs before they turned into an offroading adventure.

Has become a serious enough threat that our FDAP now tracks this. On our airplanes it is assuring you have approximately 1.1 EPR or 45% N1, depending on model, before pressing TOGA.

India Charlie

28th Dec 2016, 06:34

Forgive my ignorance here, if any...

I've seen many backtrack 180 take off's on the 737 (and 320) and as far as I can remember, the turn itself involves both engines with N1 at about 40% to accomplish the turn. I have never seen differential thrust being used on the 737 to assist a 180. This means, both engines are already symmetrically spooled and once the a/c is lined up and the PF advances the throttle levers (TOGA switch), both levers move forward in unison to T/O thrust with A/T armed, assisted by the FADEC.

I have not seen engines set to idle N1 at intersection T/Os or before T/O after completing the 180, unless T/O clearance has not been obtained or the crew is waiting for another a/c to clear the runway, a frequent scenario at Goa.

Could it be that FADEC was malfunctioning?

Mora34

28th Dec 2016, 18:56

Stop judging: Pilot of Jet Airways Goa runway crash writes a strong letter (http://www.dailyo.in/variety/jet-airways-flight-skids-off-goa-mumbai-runway-pilot-writes-strong-letter/story/1/14769.html)

737er

28th Dec 2016, 19:30

Excellent. Good on him! Wish he had added to the media to stop painting commercial aviation as unsafe and making the public fearful, when in fact it's a safety record to be damn proud of. And yes, contrary to popular diatribe, pilots actually fly airliners.

Herod

28th Dec 2016, 19:35

That letter should be on every editor's and sub-editor's wall and perhaps at the beginning of every accident/incident thread on Pprune.

core_dump

28th Dec 2016, 20:01

Stop judging: Pilot of Jet Airways Goa runway crash writes a strong letter

Just for the sake of clarity... The above-linked opinion piece was written by some random guy who had nothing to do with the incident. As for the misleading headline that appears on that site, I'm sure he had no part of it.

Hotel Tango

28th Dec 2016, 20:56

The way it is worded I don't believe for one moment that it's written by the pilot involved.

India Charlie

29th Dec 2016, 05:47

I don't think the crew would be allowed to write anything about the incident, even a sentimental piece like this, before the full enquiry was concluded. An anonymous guy from the same company perhaps.

Basic Service

29th Dec 2016, 09:10

There has been a lot of chat about how this could have happened, both an unlocked reverser or asymmetric thrust could do it ( although fadec would probably limit thrust with a deployed reverser , been a while so not sure on that one ).

Most accurate posts have suggested VMCG and governor failure. A combination of these is almost impossible to control. Usually a governor failure involves an increase in thrust as the engine "runs away" before the fadec shuts it down. As the thrust runs away the pilot instinctively corrects the yaw with rudder. So now we have, let's say right right rudder in, as the right engine runs away. Then fadec shuts it down. Now you have right rudder in with a right engine failure, end result below VMCG is exit stage right.

Not saying this happened here, but any asymmetry below VMCG would be similar.

mathewcg

30th Dec 2016, 05:43

Quite flummoxed by the runway excursion of #JetAirways Boeing 737-800, VT-JBG at GOI.

A few points:
1. Post accident pictures show the starboard thrust reverser deployed and the port reverser stowed. Is this due to the engine cowlings scraping on the ground or did actual deployment take place? Wonder what the actual position of the TR lever was?
2. Was there an uncommanded deployment of starboard reverser just as take-off power was set? Unlikely in a modern aircraft, but chances are there since aircraft was on ground with weight on wheels. But to my mind, in such a failure case the FADEC should have commanded idle power with a lot of warning bells and whistles going off...
3. Did the pilots spool up the outboard engine to assist the turn, close the levers as they line up and then stand them up to 45-50% when cleared for T/O, however the spooling down engine hasn't fully idled and so it spooled up faster than the other, resulting in a big yaw? Or did they use the TOGA button too early before lining up fully? Or was there an overspeed governor failure where the engine runs away before FADEC shuts it down?
4. Did they use reverse on the inboard engine (in this case – starboard) to assist the turn after a rather fast taxi? For this both power levers would have to be first brought to idle to escape the interlocks. But the aircraft did move forward, therefore forward thrust was available - so this scenario too is unlikely..
5. A low speed asymmetric power event is a difficult thing to handle in the night, without many visual references and no rudder control (below VMCG) being at too low a speed for rudder authority.

Waiting eagerly for proper findings on the DGCA enquiry..

Dynamite1

30th Dec 2016, 17:12

seems to have got it spot on here..
Jet Airways' pilot's act was as miraculous as landing aircraft on water (http://www.jantakareporter.com/india/jet-airways-pilots-act/88591/)

DaveReidUK

30th Dec 2016, 18:00

The most worrying thing about that "analysis" is the last line:

The author is a former Air Force officer and currently a professional pilot

vilas

31st Dec 2016, 05:49

Based on information in public domain (read hear say) dishing out accolades is just as bad as sensure of the crew. How will it look if in the inquiry some deficiency is found? No media channels said anything about the crews actions. The evacuation was pathetically handled so some pissed of passangers scared out of their wits said something there is no need for persecution mania. Ultimately accolades by brother in arms or criticism by the ignorant is not going to matter but only the conclusion of the DGCA will prevail.

vilas

31st Dec 2016, 08:55

The article mentions mandatory actions to prevent excursion as three options. All of them are simultaneous actions none of them is an option.If at all thrust reduction including reverse application on the good engine should be the first. That straightens the aircraft and obviates any need to shut down the faulty engine. This is the correct procedure and not arm chair exercise.

NukeHunt

2nd Jan 2017, 23:09

I have read elsewhere on an aviation page on a popular social media site that the crew "may" have used reverse on the no2 to assist with the 180 turn, then hit toga once lined up, but before the reverser sleeves/interlocks were fully back in place, so the increasing thrust blew the reverser back open again with said result. That was the only comment of that scenario being speculated that I've seen though.

lemme

3rd Jan 2017, 03:59

Is there anything to confirm uncommanded reverser deployment other than the pictures showing the #2 sleeves deployed (only have observed outer sleeve in pictures) and some unconfirmed accounts?

I have been studying the CFM56-7b thrust reverser (78-34-00) design to understand the barriers for uncommanded reverser deployment. it is designed to prevent this failure from occurring that which has no single pathway (assuming the throttle levers were not physically commanded to reverse thrust). A cascade of failures including multiple independent switch-controlled relays would be necessary for both sync-locks to activate, for both locking actuators to release, and to apply hydraulic power to deploy. No single hardware failure would lead to deployment (the lever/linkage itself is the only common element). There are maintenance procedures to manually deploy and override locks. The logic for on-ground or 10 feet AGL is applied as an additional interlock to the hydraulic commands.

The thrust reverser is not efficient in comparison to forward thrust, especially at low speeds (e.g. effective reverse thrust would be reduced from comparable forward thrust). For sure, there would be no forward thrust when the sleeves deploy the blocking doors (when considering yawing moment).

Until 60 knots, there should be considerable scrutiny on setting takeoff power. With the data suggesting this speed was never achieved, then the pilot monitoring should have had full attention on the engine instruments, and should have noted reverser deployment without any delay. I would have expected both throttles to be slammed to idle in this occurrence, in less than three seconds to allow for reaction, and engines spooled down about three seconds later. That would suggest that the airplane should stop accelerating within about 6 seconds from the failure occurrence. In this case, the considerable loss of directional control left the airplane still accelerating while plowing away.

Two points from the ADS-B reporting:

1) there was at least a minute from when the airplane reversed course in taxi and lined up to the when the airplane began its takeoff roll.

2) the airplane continued to accelerate after departing the runway. Three specific reports were six seconds apart, the first at runway departure (and it about six seconds from initiating the takeoff roll). From departing the runway, peak speed was reported six seconds later and speed was subsiding 12 seconds later.

framer

4th Jan 2017, 03:27

then the pilot monitoring should have had full attention on the engine instruments
I may be being a bit pedantic but if the PM had "full attention" on the engine instruments he or she would not be able to comply with the Boeing recommended SOP's for this phase of flight.
Maybe you meant that the PM should be focussing much of their attention on the engine instruments?
With your rather generous 3 seconds for recognition I think you are departing the runway with full thrust on one and none / reverse on the other if you are below 60kts.

CaptainSandL

4th Jan 2017, 08:49

Here is another possible scenario... Ruder pedal jam. Unlikely? maybe not, Boeing know about it.

737NG-FTD-25-15004
Rudder Pedal Motion Restricted
Background
An operator reported that a Rejected Take Off (RTO) was performed at 25 knots after pilot experienced stuck rudder pedals. The airplane returned to the gate safely and the flight crew reported no rudder pedal anomalies prior to takeoff roll. Maintenance found a loose flush-head fastener protruding/interfering with the rudder pedal movement (captains rudder pedal housing, left foot - inboard side). Maintenance subsequently re-torqued the fastener, performed a rudder pedal adjustment and limit test with no findings. A Boeing review of Flight Data Recorder (FDR) data confirmed the following: Right rudder pedal motion was restricted to approximately 3 degrees, Left rudder pedal motion was not restricted and Centering capability was not restricted. See the attached Illustrations for additional information.

PJ2

4th Jan 2017, 15:36

Until 60 knots, there should be considerable scrutiny on setting takeoff power. With the data suggesting this speed was never achieved, then the pilot monitoring should have had full attention on the engine instruments, and should have noted reverser deployment without any delay. I would have expected both throttles to be slammed to idle in this occurrence, in less than three seconds to allow for reaction, and engines spooled down about three seconds later.
As mentioned earlier in the thread, uncommanded deployment of either reverser just after takeoff thrust had been applied was a simulator exercise, (A320, 1992). If the takeoff thrust was not immediately reduced, the airplane headed for the weeds 100% of the time.

While an uncommanded deployment would likely be a 10^-9 occurrence, the exercise was intended to reinforce the importance of keeping one's eyes on the engine instruments when setting power and during the entire takeoff run.

vilas

4th Jan 2017, 18:11

But why would the thrust not be reduced immediately? In low speed reject even application of reverse on the available engine is airbus procedure to swing the aircraft back to the live engine side. Also there is recorded runway excursion due to sitting too far back being unable to apply differential braking. Instantaneous rudder application and thrust levers all the way back to reverse is the correct procedure.

RAT 5

4th Jan 2017, 19:25

Waiting eagerly for proper findings on the DGCA enquiry..

Indeed. Here is another incident where the operating crew survived unscathed, as did the a/c; so the subsequent enquiry should be short and swift. All this speculation about what might or might not have happened, or what the crew might have experienced or actioned etc., surely much of that is already known.

PJ2

4th Jan 2017, 20:05

Hello vilas; Re, But why would the thrust not be reduced immediately? If the engine went into reverse, yes, exactly.

Whether the engine actually went into reverse or not and if so, by what means, is still not known, so, apropos RAT_5's and others' comments, still awaiting the DGCAs account of events.

JammedStab

5th Jan 2017, 00:30

While an uncommanded deployment would likely be a 10^-9 occurrence, the exercise was intended to reinforce the importance of keeping one's eyes on the engine instruments when setting power and during the entire takeoff run.
I have to say, that I do not keep my eyes on the engine instruments during the entire takeoff run. And I don't think that it is a good idea to do so.

lomapaseo

5th Jan 2017, 00:34

While an uncommanded deployment would likely be a 10^-9 occurrence,

A little too genererous estimated above

With WOW and only two barriers the historical data would suggest something more like 10^-7 but coupled with some redundancy in the aircraft a catatrasphic result would be more like 10^-8

and some would even challenge that a third barrier could meet that 10E-9
With WOW and only two barriers the historical data would suggest something more like 10^-7 but coupled with some redundancy in the aircraft a catatrosphic result would be more like 10^-8 (WOW switch is third barrier)

Of course in this case no catastrophe resulted

PJ2

5th Jan 2017, 16:37

JammedStab, re: I have to say, that I do not keep my eyes on the engine instruments during the entire takeoff run. And I don't think that it is a good idea to do so. Yes, the statement taken literally and without the filters that normally attend knowledge, experience & airmanship is indeed too narrow for advice to young players. I was making the observation expecting that a trained & seasoned airman would know that during takeoff, focus is demanded on all aspects of the takeoff such as aircraft & engine performance, trajectory on the runway, (on centerline), etc. and not just slavishly to the engine gauges without a glance elsewhere.

lomapaseo, re: A little too genererous estimated aboveOk, well is it a difference that makes a difference?

The point being made is, it's rare, period, so I should have said "rare" and not applied an exact number.