B-738 Crash in Russia Rostov-on-Don
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As to trimming and human factors, there was a rather interesting accident in the States to a Beech 1900.
It started with a mistake made by an engineer who was working on his own on a late-night shift. He somehow reversed the way that the cable to the elevator trim was run, so that it ran in reverse back at the tail of the aircraft with the cockpit indications still showing normal sense. When he finished his task he did not check that the trim ran in the correct direction.
Next, the crew did not do a visual check of the way that the trim ran during their pre-flight walk-around.
Finally, just after take-off the PF went for nose-up trim, when the aircraft went nose-down. He continued to command nose-up until he ended up with something like 80 pounds of nose-down force on the yoke, when the aircraft then went into a terminal dive and crashed. It's interesting that at no time did the PF stop trimming, even though it should have been obvious that something was wrong with the trim system then. There was that sort of fixation on an expected outcome that has been mentioned here previously, although there was an obvious technical mistake that started that accident chain.
It will be interesting to learn what sort of interaction there was in this crash between the two flight crew, what the human factor was, since it's already been reported that the aircraft had no technical defects. If the PF had made some mistake, how did the PNF react to that, and why?
It started with a mistake made by an engineer who was working on his own on a late-night shift. He somehow reversed the way that the cable to the elevator trim was run, so that it ran in reverse back at the tail of the aircraft with the cockpit indications still showing normal sense. When he finished his task he did not check that the trim ran in the correct direction.
Next, the crew did not do a visual check of the way that the trim ran during their pre-flight walk-around.
Finally, just after take-off the PF went for nose-up trim, when the aircraft went nose-down. He continued to command nose-up until he ended up with something like 80 pounds of nose-down force on the yoke, when the aircraft then went into a terminal dive and crashed. It's interesting that at no time did the PF stop trimming, even though it should have been obvious that something was wrong with the trim system then. There was that sort of fixation on an expected outcome that has been mentioned here previously, although there was an obvious technical mistake that started that accident chain.
It will be interesting to learn what sort of interaction there was in this crash between the two flight crew, what the human factor was, since it's already been reported that the aircraft had no technical defects. If the PF had made some mistake, how did the PNF react to that, and why?
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FCOM 9.20.9
Speed Trim System
The speed trim system (STS) is a speed stability augmentation system designed to improve flight characteristics during operations with a low gross weight, aft center of gravity and high thrust when the autopilot is not engaged. The purpose of the STS is to return the airplane to a trimmed speed by commanding the stabilizer in a direction opposite the speed change. The STS monitors inputs of stabilizer position, thrust lever position, airspeed and vertical speed and then trims the stabilizer using the autopilot stabilizer trim. As the airplane speed increases or decreases from the trimmed speed, the stabilizer is commanded in the direction to return the airplane to the trimmed speed. This increases control column forces to force the airplane to return to the trimmed speed. As the airplane returns to the trimmed speed, the STS commanded stabilizer movement is removed.
STS operates most frequently during takeoffs, climb and go-arounds.
Conditions
for speed trim operation are listed below:
• Airspeed between 100 KIAS and Mach 0.5
• 10 seconds after takeoff
• 5 seconds following release of trim switches
• Autopilot not engaged
• Sensing of trim requirement
Speed Trim System
The speed trim system (STS) is a speed stability augmentation system designed to improve flight characteristics during operations with a low gross weight, aft center of gravity and high thrust when the autopilot is not engaged. The purpose of the STS is to return the airplane to a trimmed speed by commanding the stabilizer in a direction opposite the speed change. The STS monitors inputs of stabilizer position, thrust lever position, airspeed and vertical speed and then trims the stabilizer using the autopilot stabilizer trim. As the airplane speed increases or decreases from the trimmed speed, the stabilizer is commanded in the direction to return the airplane to the trimmed speed. This increases control column forces to force the airplane to return to the trimmed speed. As the airplane returns to the trimmed speed, the STS commanded stabilizer movement is removed.
STS operates most frequently during takeoffs, climb and go-arounds.
Conditions
for speed trim operation are listed below:
• Airspeed between 100 KIAS and Mach 0.5
• 10 seconds after takeoff
• 5 seconds following release of trim switches
• Autopilot not engaged
• Sensing of trim requirement
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So it is inconceivable that they managed to control the aircraft at the critical point
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Critical points?
It's a go around. No more critical than a take off.
I've done four this winter. One from an ILS at 3500 ft, one from 2000 ft on a non precision, one from ILS minima dual channel and one from ILS minima single channel.
I was not aware I was in a critical situation on any of them. No high thrust, white knuckled, struggeling to control the pitch events.
A go around is a normal procedure. Why do some of you think this is a near disaster?
Any part of the flight can become critical if you don't know what you are doing, or if your brain is working like a bowl of syrup because you are tired.
It's a go around. No more critical than a take off.
I've done four this winter. One from an ILS at 3500 ft, one from 2000 ft on a non precision, one from ILS minima dual channel and one from ILS minima single channel.
I was not aware I was in a critical situation on any of them. No high thrust, white knuckled, struggeling to control the pitch events.
A go around is a normal procedure. Why do some of you think this is a near disaster?
Any part of the flight can become critical if you don't know what you are doing, or if your brain is working like a bowl of syrup because you are tired.
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It's difficult to imagine that some versions of the 737, with almost nine thousand in all having been built so far, should be as difficult to control on a go-around as it's been said to be by some posts made here.
At its simplest, doesn't a go-around merely consist of the following?
The go-around decision and the annunciation of that to the other flight crew member.
Actuation of the TOGA switch by the PF.
Display of the desired pitch attitude for go-around on the command bars of the flight display with manual pitch to the bars by the PF.
Simultaneous manual selection of TOGA power by the PF.
Identification of positive rate of climb and the subsequent command by the PF to raise the landing gear, and so-on.
As just stated, that's a fairly routine maneuver that is practiced in every recurrent training session. It's not as though there's any real element of challenge to it as such, so that the question here seems to be "What went wrong during the execution of a routine maneuver?"
There seems to be a suggestion here that the 737 might rear up on its tail, going almost out of control, during a go-around. I don't think such behavior would be tolerated by the FAA when doing certification of the aircraft, since that would, indeed, sometimes make a go-around a a real challenge.
Is that a correct assumption, that its behavior is always relatively benign, or is the 737 really that difficult to control under certain circumstances, such as light weight, max power, and CG on the aft limit?
At its simplest, doesn't a go-around merely consist of the following?
The go-around decision and the annunciation of that to the other flight crew member.
Actuation of the TOGA switch by the PF.
Display of the desired pitch attitude for go-around on the command bars of the flight display with manual pitch to the bars by the PF.
Simultaneous manual selection of TOGA power by the PF.
Identification of positive rate of climb and the subsequent command by the PF to raise the landing gear, and so-on.
As just stated, that's a fairly routine maneuver that is practiced in every recurrent training session. It's not as though there's any real element of challenge to it as such, so that the question here seems to be "What went wrong during the execution of a routine maneuver?"
There seems to be a suggestion here that the 737 might rear up on its tail, going almost out of control, during a go-around. I don't think such behavior would be tolerated by the FAA when doing certification of the aircraft, since that would, indeed, sometimes make a go-around a a real challenge.
Is that a correct assumption, that its behavior is always relatively benign, or is the 737 really that difficult to control under certain circumstances, such as light weight, max power, and CG on the aft limit?
Last edited by chuks; 12th Apr 2016 at 03:35.
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It's a go around. No more critical than a take off.
It's difficult to imagine that some versions of the 737, with almost nine thousand in all having been built so far, should be as difficult to control on a go-around as it's been said to be by some posts made here.
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A 737 go around is very simple. The only trap is the alt aquire MCP speed window opening while you're still accelerating, which can leave you below the manouvering speed for new flap position, so you just need to keep an eye on that and select an appropriate speed.
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One problem I see is this: crews are taught to do only one GA profile. It is always practiced from DA and often - IMHO - written as a rushed manoeuvre and made worse by being very different to a normal takeoff.
ManaAdaSystem says he did an ILS GA from 3500'. That is an odd one. If that is agl, i.e. 11nm out, why not make an orbit/hold? Also it might well have been above MAA. Give that to the average trained monkey, or even from 1200', and the outcome is unpredictable. They know only one method and it doesn't fit the scenario. The a/c needs to be managed via its systems. The pilot has all the necessary tools at their disposal, but often their blinkered training hasn't included all the possibilities. Either they have not been taught or are not allowed to use them in deviation from a rigid SOP. A recipe for a screw up.
If one has correct training, good understanding and freedom to use discretion/airmanship then a GA is a benign as any takeoff. To answer why it is not you have to visit the training depts.
ManaAdaSystem says he did an ILS GA from 3500'. That is an odd one. If that is agl, i.e. 11nm out, why not make an orbit/hold? Also it might well have been above MAA. Give that to the average trained monkey, or even from 1200', and the outcome is unpredictable. They know only one method and it doesn't fit the scenario. The a/c needs to be managed via its systems. The pilot has all the necessary tools at their disposal, but often their blinkered training hasn't included all the possibilities. Either they have not been taught or are not allowed to use them in deviation from a rigid SOP. A recipe for a screw up.
If one has correct training, good understanding and freedom to use discretion/airmanship then a GA is a benign as any takeoff. To answer why it is not you have to visit the training depts.
My thoughts are that if the go around is done in a calm, controlled, deliberate manner, then as folks are suggesting, there is nothing at all beastly about the NG's behaviour ( or the -300's but it's been seven years since I flew those). That said, if too much thrust is applied, in an aircraft under say 58T, then quite a lot of physical effort will be needed to push forward on the control column to keep the attitude reasonable. If the pilot has been wound up enough to apply too much thrust, then there is a real likelyhood he or she will be wound up enough to wind in a fair whack of nose down trim in an effort to ease the ( maybe unexpected) forces on the control column. If they wind in too much, and then reduce the thrust......what happens?
Is that why the 737 has a speed trim system for operation at lite weights, aft c of g and high thrust situations? In order to satisfy the FAA certification requirements? Has this scenario been known for decades?
I don't think such behavior would be tolerated by the FAA when doing certification of the aircraft, since that would, indeed, sometimes make a go-around a a real challenge.
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Forward column pressure on a go around was only an issue on a manual go around from below 380' on an autoland app, which is unusual (one company I worked for insisted on all ILS apps being dual channel, to land manually or auto as appropriate to that airport, which could cause an issue if the cloud was below 400', and for the MAP at busy places like LGW if traffic was slow in front of you). Otherwise, it doesn't need much pressure.
Aluminium Shuffler, when you say it didn't need much forward pressure are you talking about a go around with a moderate thrust setting ( ie 85% or so depending on weight) ?
I ask because at lite weights, with an aft c of g and a fist-full of thrust ( ie mis-managed) a significant amount of forward pressure is required on the control column.
I ask because at lite weights, with an aft c of g and a fist-full of thrust ( ie mis-managed) a significant amount of forward pressure is required on the control column.
I agree with framer, which is why the big question for me is what level of automation (if any) was used on the go around and whether it was a Windshear escape manoeuvre.
There is a pretty big difference between a push of TOGA giving you reduced go around thrust and firewalling the thrust levers and getting more than full rate thrust from both engines!
There is a pretty big difference between a push of TOGA giving you reduced go around thrust and firewalling the thrust levers and getting more than full rate thrust from both engines!
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Looking at the data available, it doesn't look like anything other than an adequately (not perfectly) flown standard go-around! In other words, not an escape manoeuvre neither any signs of disorientation in the flight path leading to the nose over.
Last edited by Sciolistes; 11th Apr 2016 at 13:17.
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I joined a company that was acquiring the new NG a/c. Their GA manoeuvre/profile was carried over from their previous jet: full umph, 2 hands on control column until clean.
They then started autolands on their new toy. I pointed out that an auto GA used only +/- 88%. Thus if it was OK for a low level autopilot GA, when the a/c made its own mind up, why not copy it, manually, from a higher height and higher workload? After years of deliberation it was agreed it was not wrong and could be taught, but it was another while before it was written into 'crew guidance'. Not quite an SOP, but better than nothing.
This info was gleaned from watching automatic GA's. Now FZ don't do those; so do they realise the performance possibilities executing a safe GA with less thrust? What is their SOP for thrust on a GA, especially at an unusually high height?
If indeed they expected to land and had set the normal MAA, and then made a high GA into a low level capture with high ROC it was a recipe for a stiff challenge. It would be curious to know what was different about the first GA and what was set in MAA. It would be very interesting to hear the CVR crew briefing for both approaches. Did they anticipate a GA? Did they discuss the FL80 GA on the 1st one? Did they set 8000 in MCP on the 1st, but set the much lower correct one on 2nd attempt? Did they brief/anticipate a GA on the 2nd one; and if so, what was their Plan B afterwards. Did the Capt, in fact, fly both GA's?
Time will tell, but I hope the report will include these salient points. There has to be a significant reason why the 2nd GA went so horribly wrong and not the 1st. Indeed, was the first squeaky clean?
They then started autolands on their new toy. I pointed out that an auto GA used only +/- 88%. Thus if it was OK for a low level autopilot GA, when the a/c made its own mind up, why not copy it, manually, from a higher height and higher workload? After years of deliberation it was agreed it was not wrong and could be taught, but it was another while before it was written into 'crew guidance'. Not quite an SOP, but better than nothing.
This info was gleaned from watching automatic GA's. Now FZ don't do those; so do they realise the performance possibilities executing a safe GA with less thrust? What is their SOP for thrust on a GA, especially at an unusually high height?
If indeed they expected to land and had set the normal MAA, and then made a high GA into a low level capture with high ROC it was a recipe for a stiff challenge. It would be curious to know what was different about the first GA and what was set in MAA. It would be very interesting to hear the CVR crew briefing for both approaches. Did they anticipate a GA? Did they discuss the FL80 GA on the 1st one? Did they set 8000 in MCP on the 1st, but set the much lower correct one on 2nd attempt? Did they brief/anticipate a GA on the 2nd one; and if so, what was their Plan B afterwards. Did the Capt, in fact, fly both GA's?
Time will tell, but I hope the report will include these salient points. There has to be a significant reason why the 2nd GA went so horribly wrong and not the 1st. Indeed, was the first squeaky clean?
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An interesting article, well worthy of a read:
http://www.caa.co.za/Aviation%20Medi...rientation.pdf
http://www.caa.co.za/Aviation%20Medi...rientation.pdf
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For those who are still interested, five seconds of trim operation with the flaps up is approximately one unit of trim.
Had a play with it today in various phases of flight, after take-off (flaps up and down) and on approach (with flap 5, 15 and 30).
Didn't require any huge force to fight against it, and the F/O didn't even notice that I was doing anything at all unusual. (Before anyone says anything we were in calm conditions, good VMC and above 1000 feet, wouldn't have been messing with it near the ground with a load of passengers).
This was in the real aircraft, not a simulator. Not saying that trim didn't play a part, as to say anything with no inside knowledge would be just guessing, but hard to see how five seconds worth, or even twelve seconds worth with the flaps up, would make a dive unrecoverable.
Had a play with it today in various phases of flight, after take-off (flaps up and down) and on approach (with flap 5, 15 and 30).
Didn't require any huge force to fight against it, and the F/O didn't even notice that I was doing anything at all unusual. (Before anyone says anything we were in calm conditions, good VMC and above 1000 feet, wouldn't have been messing with it near the ground with a load of passengers).
This was in the real aircraft, not a simulator. Not saying that trim didn't play a part, as to say anything with no inside knowledge would be just guessing, but hard to see how five seconds worth, or even twelve seconds worth with the flaps up, would make a dive unrecoverable.
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"At a height of 900 m there was a simultaneous control column nose down input and stabilizer 5-degree nose down deflection, resulting in abrupt descent with negative vertical acceleration of -1g."
makes it even more bizarre.
Good explanation of spatial dis. in part. somatogravic illusions: Spatial Disorientation - SKYbrary Aviation Safety
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Well, illusion of climbing occurs when plane isn't really climbing or not climbing as fast/steep as pilot perceives. Otherwise it wouldn't be an illusion.
Good explanation of spatial dis. in part. somatogravic illusions: Spatial Disorientation - SKYbrary Aviation Safety
Good explanation of spatial dis. in part. somatogravic illusions: Spatial Disorientation - SKYbrary Aviation Safety
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But it was climbing, climbing consistently and apparently correctly. So it would seem they were not disorientated and the aircraft was completely under control. You can even see nicely controlled acceleration phase. That is a very strange kind of illusion.
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The thing about somatogravic illusion is that while it often involves an acceleration of the aircraft that acts upon the vestibular system, it can also involve a direct acceleration of that system caused by a rapid change of head position, something as simple as a quick drop of the head to look for an object in the cockpit such as a pen or a chart.
Given the fairly steady state of the aircraft prior to its rapid final descent, that might be a plausible explanation for one part of what initiated the accident sequence.
Given the fairly steady state of the aircraft prior to its rapid final descent, that might be a plausible explanation for one part of what initiated the accident sequence.