737-500 missing in Indonesia

[Starbear]

Spot on Bleve. I have even recommended pilots consider such steps when obviously confused as to which engine has failed, quite often when manually or even automatically flying a holding pattern. Not recommened very close to the ground (!) but very effective in most other phases and can be completed in a few seconds and very effective in confirming the live engine(s) an so required rudder input.

[ExRR]

Originally Posted by 42go

I suspect, David, it is called "Passing through the inverted"? Done any aerobatics?

Whilst not commenting on this accident the above "Done any aerobatics" reminds me of training we received at RR some 50+ years ago. We were sent up in a Dove, each seat kitted out with an instrument panel from which we were to note readings for instance at pre-stall and other conditions. One of those conditions involved the pilot putting both engines on full power then cutting one out completely and leaving the aircraft to do its thing for, well it felt like forever, whilst we were supposed to calmly note the various sensor readings.

It's a bit akin to getting into a skid in a car, everything happens very quickly unless you know what you are doing.

[bsieker]

Originally Posted by FlyingStone

That's not true. 737 A/T has two servomechanisms, one per each lever. Have a look at this BITE test, particularly around 0:45, where you will see that A/T can move each thrust lever separately.

This functionality is required to synchronize the engine RPM, as the same thrust lever angle might not result in exactly the same N1, depending on many factors, particularly with these hydromechanically-controlled engines.

Indeed, the OM says in the Autothrottle System description:

The A/T moves the thrust levers with a separate servo motor on each thrust lever.

So I would expect this to be common knowledge among 737 Classic drivers.

I wonder where the seemingly widespread idea originates that there is a single motor driving both levers.

It also seems that a "Thrust Split Monitor" is available as an option, described as follows:

Additionally, on some airplanes, a thrust split monitor disengages the autothrottle if autopilot roll control requires significant spoiler deployment and thrust levers become separated. The thrust split monitor is active when flaps are less than 15, and the A/T is not engaged in the takeoff or go-around mode.

How common is this thrust split monitor? It seems it might have been helpful in this case. The very fact that it was available indicates that someone thought it might be a good idea in some cases, but I know nothing about its history.

[BuzzBox]

Originally Posted by fdr

The left thrust lever has operated correctly; the problem is that in response to a thrust reduction command, when the climb mode of FLCH/VNAV - THR; changing to ALT CAP -SPD, that gives a thrust reduction.

The aircraft was initially cleared to climb unrestricted to FL290. At 14:39:01, ATC instructed the aircraft to stop the climb at 11,000 ft due to traffic. The preliminary report states the L thrust lever started reducing at 14:38:42, ie BEFORE the aircraft was instructed to stop the climb. Does that not rule out a thrust reduction caused by an ALT CAP-SPD mode change?

[BDAttitude]

Originally Posted by fdr

... It is conceivable that the aircraft recorder ends with the TLs still split, LH at idle, RH at climb thrust. There are surprisingly few ways to get from A to B in the time available; from the first report, a roll excursion was likely. reminiscent of Sharm Al Sheik.

That was the scenario I had in mind, when asking what a recovery with split thrust would look like.

[Centaurus]

The FDR has given investigators definitive information of an autothrottle defect where a split throttle situation occurred. To a competent crew it should be nothing more than a minor technical inconvenience. Yet in this case the incompetency of the crew to handle a split throttle situation must surely raise eyebrows.

Described in Post 310 of this thread is the utter confusion I witnessed among the two pilots in the simulator - in particular the very experienced captain - when an autothrottle clutch motor was failed while both thrust levers were at idle as part of speed control. As power was increased with flap and gear extension and only one throttle opened up, the stunned crew did nothing and watched the aircraft roll into a spiral dive to oblivion.

At the time I found it hard to believe such a simple defect could quickly turn into a major loss of control disaster. Now it has happened in real life in the form of the Sriwijaya 737. One wonders how many other experienced airline captains are out there that simply can't fly.

[Check Airman]

This preliminary report is eerily similar to what Centaurus wrote in this post.

Why is automation dependency encouraged in modern aviation ?

[Check Airman]

Centaurus

I think I must have been writing my post and searching for the link, as you typed yours. Thank you for your words of wisdom. It really underscores the need for less automation. Especially after covid.

[Denti]

And yet managers insist, especially as they know we are all a bit rusty, to use automation as much as possible, and of course most pilots do.

[Uplinker]

@ FlyingStone and bieseker:

Thank you both, my mistake re number of motors, (corrected). Only flew it for one season but I should have checked before posting. General hypothesis regarding lever asymmetry remains.

[Old King Coal]

Some flying rules for flying Boeing's that have served me well:

1. Never totally rely on the automatics to do the right thing when you need or expect them to (be that the auto-pilot and / or the auto-throttle). Assume that those auto-bastards are out to get you!
2. Any time that the thrust is changing keep your hand on the thrust levers and if you get a mismatch / throttle stagger or the levers don't move as & when expected, do something about it (disconnecting the automatics as required). The same applies if the control yoke suggests that the aircraft is not in trim [with typical reasons for that being: asymmetric thrust (why?), and / or asymmetric fuel load between the wing tanks (fuel leak maybe?), and / or that the rudder trim is not set correctly (why would that be?), and / or that the silly sod in the other seat is resting their foot on a rudder pedal (****!)... use DODAR]... figure out why, do something about it if so required and keep your colleague in the loop.
3. Airmanship applies ! (though I'm well aware that the 'A' word is a dirty word in some airlines).

bsieker... fwiw, almost every time I go to work (in a B737 Classic) I've got matched N1's but with thrust levers that are spilt (see pic)... and yes I know all about the throttle stagger limits, and yes I do write it in the TechLog (and take pics of it too), and yes the engineers fiddle about and try to fix it, but hey ho what to do eh?! (see the rules above)

[SteinarN]

Old King Coal
Is that your pic? Does it happen the levers are that much split with the same N1?

[Uplinker]

Check Airman

Or highlights the need for better automation. I am surprised that something as benign as a large engine asymmetry (however caused), can potentially result in a loss of control. Why isn't the rudder controlled by the auto-pilot?

[GBV]

BuzzBox

I believe you are correct. Probably the problem wasn’t the Auto Throttle but the engines settings/readings. Something similar to Aeroflot-Nord B737-500 crash in Perm in 2008. Have a look at this throttle stagger:

Crash: Aeroflot-Nord B735 at Perm on Sep 14th 2008, impacted ground while on approach to Perm

Anyway, I absolutely agree with Old King Coal, assume that those auto-bastards are out to get you!

[zoigberg]

Originally Posted by SteinarN

Old King Coal
Is that your pic? Does it happen the levers are that much split with the same N1?

That looks a little beyond limits that our engineers would accept when I was flying these. Maximum was the handle width so still the best part of an inch on some older -300s and -500s

[Herod]

Auto-throttle malfunction during take-off, and again during the climb. And it was re-instated twice, and not monitored. Surely, disconnect the darn thing, and fly the sector with manual throttle.. Maybe I'm an old dinosaur.

[Kirks gusset]

The crew seemed hell bent on using a defective A/T system, the roll at 4.5 degrees nose up could have easily been due to them yanking back the thrust levers and stalling the AC, in any event, Boeing recommend disconnecting the A/T, once again this is a case of Pilot Error. Basic airmanship seems to have been lost and without the CVR it's just speculation as to what was going on. This was, according to their "hours" an experienced crew, which again can be a recipe for disaster if the cockpit gradient is slight, Captain is described as "kind Pilot", usually this ex Military guys are assertive, the plot thickens.

[sceh]

One thing's sure and that is that with the kind of leadership as illustrated in the report, nothing is going to get better. Any of their pilots that accept this kind of tosh will, I hope, never fly me.

The Chief Pilot of Sriwijaya Air issued the following notice to pilots on 20 January 2021: This notice reach you as a call toward the safe flight. With recent tragedy, we urge all pilots to raise awareness and keep the highest professionalism and discipline on your duty. This can be fulfilled with many guidance that we had: • Follow Operating Experience guidance. 27 • Review Training Aid. • Awareness of aircraft position, attitude, aircraft systems by active monitoring the state of aircraft on every phase of flight. • Awareness of aircraft configuration, thrust lever position/power setting and flight control system modes, anytime airplane deviate from its intended state must be corrected immediately. • Cockpit crew is responsible for entering clear and accurate write-ups of any discrepancies, including any incident or anomaly observation in AML, use of FRM (737NG) and/or describe discrepancy information comprehensively.

I suppose it is nice of him to remind them that professionalism and discipline on duty but it is hardly a strict set of orders

[Teddy Robinson]

So this had been written up in the ATL, cleared with "cleaned contacts tested found satis report further" or similar .... then ...
it retards a TL during the takeoff, and again at 8000 feet ....

I really have to ask why the AT was not disengaged by the second rollback at the latest.
Is the B737-5 really that difficult to fly without it ?

The answer has to be no.

[lomapaseo]

In the preceding discussion I see two issues in blaming it on the pilots.

1. is the issue the lack of normal skills in recovering from asymmetrical thrust?
2. Or is the issue the failure to recognize that thrust asymmetry is happening until too late?

the corrective actions the industry must address are key to identifying some of the links in this accident without regard to blame or demonizing the crew.