PDA

View Full Version : Jammed Elevator on takeoff B737


skyeuropecapt
20th Feb 2010, 08:36
Dear all,

If you ever encounter a jammed elevator during the take off roll what would you do?
you are PF and PM calls for rotation.No chance as the elevator is blocked , you give the PM controls and ask him to rotate but without success...
This situation was given to me for the first time in a training Sim..
As it was not a balance field i rejected about 2 secs passed V1 and managed to take aircraft to a full stop with remaining runway.

My question is , wouldnt it be safer to overrun the runway at low speed than trying to manage such a problem at low speed and low altitude having just the stabilizer trim and very limited elevator control.

Shoot!!!:ooh:

Avenger
20th Feb 2010, 12:40
Ok, that's a nasty trick in the sim, maybe you could have noticed this before V1 when you change the pressure on the elevators as speed increases., At V1 if you didn't notice and cant get airbourne at VR.. not many choices, rejection slightly after V1 may be an option, (if not and if you can't move the elevators at all it suggest a serious jam as the realease mechanism should allow an overide), get the PM to move the stab trim manually if the electric trim has stopped. If you rotate on stab trim be very careful, Boeing advises against use of stab trim below 400' incase of runaways.
I would favour a rejection at V1 or even plus a few knots, this may be safer than the alternatives of not being able to climb to screen height and beyond.
Still food for thought..no concise answers, just the route most likely to lead to a successful outcome (or less damage)

fdr
22nd Feb 2010, 08:05
I have had a jammed elevator airborne, and can attest you don't want it.

On the balance of risks. going off the end at moderate speed is what I would consider the least risk outcome. If you manage to get airborne and are unable to regain a trimmed flight condition, in a fairly short period of time available, then the outcome is disastrous.

For the B737, the manufacturers guidance in the rejected takeoff procedure is that unable to fly is a (fairly obvious) cause to reject. This is usually worded as the period from 80Kts to V1, however it begs the question what about post V1... when the plane still won't fly.

(If you recall the DC-10 @ RJFF, 13 June 1996, GA-865, which rejected after V1 on Rwy 16. The center engine N1 had let go and peppered the hydraulic systems. The captain was criticized at the time for rejecting after commencing the rotate, however many years later it was accepted that the captain had felt the controls degrading as a result of the hydraulic loss, and concluded the aircraft was unflyable. The wreckage showed similar impacts across the horizontal stabilizers as UA-232 had. IIRC the captain subsequently died about 5 years later, but had been acknowledged by the investigators as having acted correctly).

You don't have a lot of time to come up with an answer where both outcomes are potentially dangerous.

Your decision in the sim speaks for itself.

FDR

yankeeclipper747
22nd Feb 2010, 08:24
My solution is simple: I always do an elevator control check at 80kts. It's been part of my personal technique for the last 20 years. At that speed there is enough airflow to notice some control response and reject safely if something isn't right.

Centaurus
22nd Feb 2010, 14:14
You don't have a lot of time to come up with an answer where both outcomes are potentially dangerous.


And what if you have a hard over rudder just as an engine fails? or both sets of brakes fail on manual reversion landing while you are trying to tug both reverse levers into reverse at same time a burst tyre occurs in left outboard wheel.

No point in frightening the horses in these useless speculations. There are greater priorities in simulator training than stressing crews with out of this world emergencies.

safetypee
22nd Feb 2010, 14:44
This appears to be one of those problems where pilots may be tempted to ‘out think’ the safe guards within aircraft certification. In these cases, first, start by following the manufacturers’ procedures and advice, and second, don’t dream up new personal procedures to address ‘hypothetical’ (at least very low probability) circumstances.

Aircraft certification requirements (CS 25 / FAR 25) require a very high level of reliability / redundancy for flight controls. A jammed elevator has to be considered, and an alterative means of control provided; the subsequent action should not require excessive strength or more than average skill.

Most aspects of system certification are based on probability – exposure to, and the severity of the event (CS 25.1309).
An aircraft must be able to survive an elevator jam at rotate; the alternative of stopping is usually deemed a very high risk.
A stop option above V1 should never be associated with an RTO; there are significantly different circumstances (situation assessment and decision making) and risks.
Pilots should not believe that they can evaluate rare and possibly unforeseen circumstances at the time of the event, particularly where high risk (or perceived risk) can bias judgement – apart from the stress of surprise. The solution is to be knowledgeable of procedures and advice, and skilled in the selection and execution of the most appropriate action for the situation; again knowledge - know what, when, how.

What is the purpose of demonstrating this failure in the simulator?
Primarily it should be to aid identification of the situation and then select and follow the procedures. The failure provides opportunity to improved flying skills with degraded control and then situation assessment and decision making – divert, heavy wt landing, limiting configuration.
Simulation should not be used to catch people out or present situations or advice which results in an accident. Simulators can and should be used to improve skill and confidence, familiarity with failures, and situation assessment. There should be less focus on specific ‘what ifs’ and more emphasis on generic procedures such as controlling surprise, not jumping to false conclusions, and acting rationally – not reinventing the wheel. Centaurus :ok:

So, not being qualified in the 737, what are the procedures for that aircraft?
Most, if not all the aircraft which I flew did not require the pilot to use trim to get airborne and establish initial control; thereafter trim (and flap) was a powerful control which had to be used carefully.

skyeuropecapt
22nd Feb 2010, 15:27
Thanks to all who have replied so far.
I will keep in mind the 80 kts 'elevator check' as an extra chance to spot such unrealistic but possible problem.
Reason why i didnt 'feel it' at 80 kts is because i normally dont apply elevator pressure on take off unless there is substantial crosswind.

Centaurus: I am not the instructor, and it was a training without debriefing just prior to an airline sim check for a job.

Safetypee:I agree with you as the rules are clear about reject or not.It just happened that i was physically unable to lift the aircraft and was caught by surprise,(first time i had that in the sim).
In the few seconds i had,i knew how difficult it would be to safely lift the aircraft (there was no movement at all of the column...at least on mine,not even a dead band..)and knowing how boeing highly suggest to avoid a go around with a jammed elevator, i decided to reject.

the instructor told me to rotate using the trim which i did, about 100 feet ,from behind my seat he decided to show me how the trim works and the aircraft started to pitch in a way that he decided to freeze the sim and start a new exercice.:suspect:

I am not here to discuss what instructors should do or not ,,,just to have an idea if someone may have done such a takeoff with only stabilizer trim in (no elevator at all) in the sim.

Since i got the job, i will ask in my next opc the chance to practice this exercise and rotate with the trim only and see how it goes....just out of interest...

safetypee
23rd Feb 2010, 02:38
skyeuropecapt, no criticism here, just my interest in human behaviour / operational techniques, SOPs, etc.

During takeoff, at rotate you identified a problem with the elevator with the apparent inability to raise the nose. You considered a recommendation not to fly a go-around in your decision to stop.
That was interesting logic, an odd recall of memory; I wonder where that link originated from; training, manuals, hearsay, and why apply out of context advice to a situation with an unresolved failure. The human mind is a mysterious thing, particularly if not kept under control.

I have an old copy of a 737-400 QRH (2005). The jammed elevator drill is halfway down the page titled “Jammed or restricted flight controls”.
The drill states “overpower …”, “use maximum force … both pilots …” etc. There is no mention of using trim at this stage, and even when suggested, it is only used to offload control forces, not to provide control (also given as a table in the training manual).
The training manual also warns of the hazards of trim use during a normal takeoff – tail strike.
If the above is essentially correct then the instructors advice – use trim to rotate – may be an error or misinterpretation of existing advice; the advice could be hazardous.

The drill which I have includes a requirement to review the go-around procedure before commencing an approach. I cannot find any recommendation suggesting that the manoeuvre should not be flown with a jammed elevator if required. The training manual suggests ‘avoidance if at all possible’.

If the above aspects are relevant to your questions, then I suggest some re-reading of the manuals and QRH, and a discussion with other training staff / senior Captains to establish some of the facts about this subject.

In more general terms (other aircraft), use of trim for control has many potential problems; - what part of the control system is jammed, which way to move the trim, how far / fast should the trim be moved.
Trim systems are very powerful and although in exceptional circumstances they can be used for control, they can equally result in loss of control.

Re an 80kt control check; don’t invent a new check unless recommended by the manufacturer. What might be acceptable in a nose-heavy 747, could create problems in a smaller aft-loaded aircraft if the nosewheel was inadvertently raised in slippery crosswind conditions.

Sciolistes
23rd Feb 2010, 03:24
My solution is simple: I always do an elevator control check at 80kts. It's been part of my personal technique for the last 20 years. At that speed there is enough airflow to notice some control response and reject safely if something isn't right.
Wouldn't the standard procedure of pushing the control column forward during the early part of the take off run achieve the same thing? Or are we talking about a specific type of jam that is only apparent when you try to select up elevator beyond the neutral position?

skyeuropecapt
23rd Feb 2010, 06:54
The drill states “overpower …”, “use maximum force … both pilots …” etc. There is no mention of using trim at this stage, and even when suggested, it is only used to offload control forces, not to provide control (also given as a table in the training manual).

Safetepee: I FULLY agree with you, it may have been a sim problem, I wasnt able to overpower it hence i gave controls to thE FO (also a captain).He wasnt able to break the jam either.So at that point the only way to lift the nose would have been by using stabiliser trim ,(definitively not by changing flaps setting as mentionned above as this aint a cessna trying to make its screen eight by a couple of feet )and since i am no test pilot nor was i ever trained for such a failure,with a non balanced field, i at that moment decided to reject.
If boeing states that pilots should avoid a go around if at all possible makes me think how tricky that could be....even with limited elevator control.

Once again, the sim was a basic rush of all kind of failures with no sense whatsorever,just to apparently warm me up for what was a well conducted,planned profile of multiple failures and manual skills testing by the state CAA examinor.

I understand and agree with all of you concerning the purpose of sims,sop training,failures which make sense (especially multiple ones..)

An elevator 'check' at 80 kts was mentioned and i somehow think its a good idea but that only includes a movement of the control column from down to the neutral position,,not to up.as that would be quite non standard.
Boeing states that forward pressure control column is a not a standard procedure,(ie not for every t/o),just in case of crosswind and a if the runway is wet or slippery conditions.

Once again, the jammed was not breakable, wether its a sim problem or me lacking gym practice..i dont know...so id like to hear from some who practiced it during takeoff in sim and how successfull it turned out to be until i have the chance to practice it myself.

regards

skyeuropecapt
23rd Feb 2010, 07:11
from Boeing Flight crew training manual:

'For those controls without override features(maybe sim setting),limited flight control surface, deflection occurs when CONSIDERABLE force is applied to the flight control(.....) this response MAY be sufficient for airplane control and landing.'

from boeing FCTM:
'If the elevator is known or suspected to be jammed,a go around SHOULD BE AVOIDED IF AT ALL POSSIBLE.'

IRRenewal
23rd Feb 2010, 08:27
Boeing states that forward pressure control column is a not a standard procedure,(ie not for every t/o),just in case of crosswind and a if the runway is wet or slippery conditions.

From the B737NG FCTM Rev 8, page 3.6:

Light forward pressure is held on the control column. Keep the airplane on the centerline with rudder pedal steering and rudder. The rudder becomes effective between 40 and 60 Knots.

And page 3.8:

Above 80 Knots, relax the forward control column pressure to the neutral position.

No mention of X-wind or slippery conditions. Had you followed this Boeing guidance you might have spotted something was wrong around 80 Kts. (Unless the instructor jams the elevator between 80Kts and rotate, in which case he/she needs to get a life.)

Where did you get the information that holding forward pressure on the control column during the initial phase of the T/O run is NOT a Boeing recommendation? You are quoting the FCTM in you last post, so you must have access to it.

skyeuropecapt
23rd Feb 2010, 09:15
ok,
FCOM : Initial take off roll section p3.4 states' Light forward pressure is held' so YES somehow it is a standard procedure eventhough i dont see it as quite so necessary.I never used light forward pressure with dry runway ...as i believe my nose wheel is steering properly and well connected to the asphalt.
However if the runway is slippery, the light forward pressure below 80 kts will be useful in increasing the nose wheel steering effectiveness.

I do stand to be corrected as usual:E

IRRENEWAL..i didnt mean to write in my earlier post 'boeing states' but boeing statement....sorry i have a poor english too:(

IRRenewal
23rd Feb 2010, 15:50
skyeuropecapt,

May I politely suggest that you don't 'invent' your own procedures.

Brian Abraham
24th Feb 2010, 02:18
No point in frightening the horses in these useless speculations. There are greater priorities in simulator training than stressing crews with out of this world emergencies.
I know simulator time is at a premium and crews would like more, but sometimes the dog of fate............. Hawker Siddeley test pilot Desmond Penrose was doing an acceptance flight on a BEA Trident and conducting stalls in the landing configuration when he found the elevators locked solid - caused by an extraneous bolt jamming the controls. Safe landing made using power to control pitch.

safetypee
24th Feb 2010, 02:26
This thread has identified some interesting aspects of training and operation.
1. Does the particular simulator correctly represent a jammed control system?
2. What is the purpose of simulating a jammed control during take off; what are the training objectives of this event?
3. Has a new procedure been generated just to overcome possible simulator deficiencies?

1. The manuals indicate that a jam either in the control input or at the control surface is unlikely, but if a jam did occurred, then alternative split systems or reversion to manual will regain sufficient control. The simulation as described appears to be incorrect.
The drill for a jammed system appears to start with applying force (after checking the autopilot is disengaged – interesting see the Air NZ 777 thread). Control is achieved with control column movement; trim is used as a follow up input to relieve control force - as per normal flight.
The problem during GA appears to be due to the ‘large’ and ‘rapid’ change in trim due thrust increase.
The takeoff trim setting is usually such that the aircraft is reasonably in trim at V2 – V2+10; there should not be any change in trim due to thrust change, thus no trim input would be required until the aircraft accelerates. Any inappropriate use of trim would put the aircraft out of trim

2. As stated in an earlier post, I would expect simulator training to demonstrate a failure, practice the identification and selection of appropriate action, and then practice the subsequent flight procedures. Thus the objectives might be to present knowledge, practice assessment skills, and then practice flight and planning skills.

3. I hope that the procedure was not introduced to cure a simulator deficiency, but I have seen examples of this elsewhere.

I joined this thread on the back of earlier replies which generally agreed with the decision to discontinue the takeoff and attempt to stop within the remaining runway distance. In this context, note that the simulator may not correctly represent stopping performance, particularly on a wet runway.
Recent information now suggests that the decision was incorrect. This view, particularly the judgement of correct/incorrect is made in hindsight, but as in most accidents/incidents, the decision in the eyes of the decision maker at that time is ‘always’ correct. The decision would be based on what is seen, assessed, and understood, - as clearly explained by skyeuropecapt earlier.
It appears to me that in this aircraft there is no need to consider a jammed control as a reason not to fly when identified at and after Vr; thus removing the possibility of an overrun accident. In some aircraft types it might be assumed that a jammed control system is identifiable before V1 and thus an RTO would be justifiable, but not later as modern aircraft certification requirements provide alternative courses of action.

I too would like to understand if this simulator is correct, exactly how does the aircraft behave at rotate, how might the reported control forces be related to other flight operations (e.g. stick force equal to 20kts out of trim) and thus aid crews to better understand what to expect with such a failure?
A good thread for learning … … and thinking.


P.S. from FCTM - ‘light forward pressure’ becomes ‘forward pressure’ in the Adverse Runway Conditions section. Perhaps it’s all relative; not necessarily new procedures, just different interpretations of manuals – like different assessments of a situation.
Errors in Aviation Decision Making. (www.dcs.gla.ac.uk/~johnson/papers/seattle_hessd/judithlynne-p.pdf)

skyeuropecapt
24th Feb 2010, 05:20
IRRENEWAL,

Safetypee 's last post clearly laid down what my questions were and what i expected to know from this thread.
He even spotted the reason behind my own 'procedures' as you mentioned: here is his quote if you dont mind safetypee:

'P.S. from FCTM - ‘light forward pressure’ becomes ‘forward pressure’ in the Adverse Runway Conditions section. Perhaps it’s all relative; not necessarily new procedures, just different interpretations of manuals – like different assessments of a situation.'

I will come back on this thread when after i had the chance to experience it properly in my next sim session.
Safetypee....the floor is yours.:E

rudderrudderrat
24th Feb 2010, 10:04
Hi skyeurocapt,

That sim scenario is unrealistic in it's failure. You did a flight control check on taxi out. The chance of both load paths jamming on the take off roll is so remote you don't need to do any non standard 80kts checking. The sim fault would presumably be inserted at a higher speed.

I suspect the sim examiner was looking to see if you appreciate your performance, by the experience you have gained, of what the remaining runway looks like at V1. If your runway was infinitely long, then your maximum V1 would be much higher than the one you had bugged. Once you had identified the control jam, the options were :
1) to attempt getting airborne using some untried and not recommended method, or:
2) to realise there was sufficient runway ahead to sensibly attempt an RTO.

I think the sim examiner was seeing if you would sit at a set of broken red traffic lights all night, or proceed with caution when you had realised the problem. I'd say you made the right decision.

411A
24th Feb 2010, 16:42
If you ever encounter a jammed elevator during the take off roll what would you do?


Don't fly a 737, however...the type I do fly has provisions for this.
Split the spoilers for pitch control.
Practised in the sim from time to time...works good.
DAL had one for real at KSAN, worked good then, as well.
Type...TriStar.:)

Centaurus
25th Feb 2010, 13:01
There have been several reports over the years of incorrectly placed cargo in the cargo holds that resulted in an initial difficulty for the pilot to rotate at VR. This shows out as nothing happens when you start the rotation and it seems if the nose-wheel is not coming off the ground. Usually if you heave more strongly on the wheel the aircraft (737) gets airborne and once into the initial climb use of stab trim corrects the nose heavy situation. I recall a recent 737 incident at Manchester where the F/O perceived a stuck elevator during his attempt at rotation and called to the captain to take over. The captain perceived the same difficulty and promptly aborted some time after VR speed. Fortunately they were able to stop in time. If I recall correctly the problem was the stab trim had not been set correctly and thus stick forces on rotation fooled both pilots.

I had a similar situation decades ago when the load had not been distributed correctly (unknown to me) and at VR despite heaving back literally the nose wheel stayed in contact with the runway. Another firmer heave back got the aircraft airborne around V2 plus 20 knots but not before a check captain in the jump seat actually panicked and screamed for me to rotate. I kid you not - the silly blighter frightened the heck out of me more with his shouting, than the delayed un-stick. At the subsequent court of inquiry held in the chief pilots office with tea and bikkies not supplied, I was accused of "forgetting" to rotate. Office politics was strong in that airline - but enough of that.

In fact, when we landed a few hours later at destination and weighed the cargo and checked its true distribution, the stab trim setting which should have been set (as against what we had worked out for the assumed distribution) was only around one unit difference. But the stick force to rotate was far harder than I ever would have thought.

There had been a similar, but far more potentially dangerous event, in a company 727 that refused to respond to elevator input at Vr. The pilot hit the stab trim and managed to claw his way into the air. Turned out the load had been understated on the load sheet by several thousands of kgs and the CG was outside the forward limit.

It got me thinking that where there is difficulty in rotation, it could cause the pilot to think the elevator had jammed. Things happen so quickly. In turn he may be tempted to make an instant (but possibly unnecessary) abort and by then V1 has long since passed and likely V2 as well.

For some years now, I have briefed pilots undergoing type ratings on the 737 of this insidious danger of incorrect stab trim setting which may cause a stick force reaction at VR.

In the simulator I operate, it is not possible to alter the CG enough to cause a significantly nose heavy stick force on rotation. I believe however, the possibility of this type of event happening once or twice in a pilots career is probably quite high.

But in the simulator how does one "fake" the stick force so that an actual very heavy pull back on the control column is needed to get airborne - apart from the obvious one of having the PNF push forward on the wheel while the pilot tries to pull back. It is all very well recounting on what could happen one day, but a picture or demonstration is worth a thousand words.

Now this may invoke snorts of derision from readers but one method to set the scene is by winding the stab trim fully forward before take off in the simulator. Of course the crew are briefed it is a training exercise with no surprises. The aurul warn C/B is pulled to silence the configuration warning. At Vr the pilot will find the initial pull back has no effect and the aircraft stays on the runway while accelerating well beyond V2. A strong smooth heave will eventually lift the nose and the aircraft gets airborne. Rapid operation of stab trim back to normal setting occurs in the climb and the lesson is over.

The object of the exercise is to have the pilot experience very heavy stick force at VR and still get airborne - rather than risk an instant gut-feeling decision to abort because of a perceived "unusually heavy stick force". I appreciate this may be considered a highly non-standard way of doing things. But one thing is for sure, and that is the resultant stick forces were identical to that I experienced during my incident in a 737 many years earlier. Necessity being the mother of invention, perhaps?

Comments invited of course but preferably constructive rather than derisory.
Maybe some expert can offer another solution how to introduce a very heavy nose heavy stick force in the simulator at VR but using normal take off stab trim setting. I believe it is an important part of type rating training.

Port Strobe
25th Feb 2010, 13:40
Centaurus
winding the stab trim fully forward before take off in the simulator. Of course the crew are briefed it is a training exercise with no surprises. The aurul warn C/B is pulled to silence the configuration warning

Scratching at fading memories here but isn't the range of the main electric trim on the 737 less than the full range of manual trim wheel inputs, hence full nose down trim will be unrecoverable without manual trim wheel input?

On the subject, if the trim setting is on the forward limit of the green band (so no take of configuration warning upon setting take off thrust) does that guarantee that there is sufficient elevator authority at Vr to initiate rotation?

yankeeclipper747
25th Feb 2010, 22:17
Hi Sciolistes, 80 Kts because the elevator becomes responsive then. At the start of the TO roll, you won't know if there is any control surface movement. At 80 kts you will

Kirks gusset
25th Feb 2010, 22:30
Nearly right Port Strobe, the electric trim is forward limited, to move outside this range you have to pull the stab trim cutout switches and wind the stab trim fwd manually. If you restore the stab trim cut outs, the electric trim will be available from the fully fwd position you are now in to wind the stab trim back to the normal range.

Thie exercise ( jammed elevator) was probably introduced as the incorrect technique was applied during the take off roll.

fdr
25th Feb 2010, 23:32
Hi.

if the elevator control moves full deflection without developing a pitch rate, the likelihood is the aircraft is out of trim, by either an erroneous stabiliser setting, or an incorrect load. For the first case, the aircraft is designed to have adequate elevator authority to override the stabiliser setting. For the erroneous cg, in most cases there is adequate elevator and stabiliser available to fly the aircraft, but rotation will be at a higher speed due to the delay in response.

The cg error can be either excessively forward or aft:

for the aft cg, the aircraft will have a noticeable poor nosewheel steering response at almost all speeds, with a fair bit of scuffing occurring. If that doesn't trigger some concern, on power application on most aircraft (not the MD11/DC10) the nose will pitch up, extreme cases. In all cases the pitch attitude will increase on the roll without command. On one case evaluated, the pitch up occurred on thrust application, and the nose wheel was off the ground before 60 KIAS, and the aircraft lifted off without control input about 5 kts before V1. The aircraft was dynamically unstable, but only mildly so, and the crew engaged the autopilot at low altitude which coped with the instability. In that case the crew then cleaned up.... and continued to destination... and the cg got worse along the way. on landing the aircraft pitched up after touchdown and went off the side of the runway at low speed. That aircraft had a cg 12%MAC aft of the normal envelope, and 2% further aft than ever tested by the manufacturer. The data showed that the AP was responding to the instability constantly during the cruise, and the possibility existed that a disengagement in cruise would have resulted in structural overload through a PIO. Don't recommend flying an out of trim aircraft at speed or high mach, altitude....

On another aft cg case, the aircraft pitched up on thrust application and the tail hit the ground, below 50KIAS. the crew rejected the takeoff, but were able to taxi back...

For the forward cg case, it is only going to be apparent at rotate; on one case evaluated, the elevators moved correctly to their commanded position, but there was no pitch rate initially, with increasing pitch at about Vr+20KIAS with full elevator application. The aircraft cleanup was delayed until the crew confirmed the trim error, and evaluated that the configuration change would not adversely affect the trim case. Normal fuel burn placed the cg shift beneficially, on landing the aircraft used limited flap and full manual trim, and was still out of trim but controllable in pitch.

A jammed elevator is indicated by restricted movement of the elevator control on a conventional control system, and may be either in the control runs or the actuator/surface. Most mechanical systems have a control system split available, where override will disconnect the L & R control channels to allow freedom of movement. FBW systems introduce alternative failure modes, but for the B777 are basically conventional, the Airbus is different....

On a 4 engine aircraft at heavy/limiting weights, a jam noted at Vr is going to be bad news. The time available for evaluation and response is probably less than that available before crossing the golf course.

On a 2 engine aircraft, the situation is a little better, and there may be adequate time to apply nose up trim sufficient to fly the aircraft off the ground. I would think your ball park figure is going to be in the order of 3-4 units of additional ANU trim to get the plane to respond, and that will take some time to run, probably 8-10 seconds. From that time, the aircraft will start to pitch After liftoff, the aircraft will have excessive ANU trim and will continue to pitch up, and will need a return to near the original TO trim position. If the speed gets out of sorts, roll may be advantageous in maintaining speed until the stab trim has been set correctly.

If you have proceeded with a takeoff, and get airborne, then limiting configuration changes may be wise. The aircraft AP system particularly ones with CWS functionality may have the ability to bypass the control run if that is the cause of the jam, and act directly to the elevator hydraulic control servo (at least one type does that).

time wise, the 4 engine aircraft at balance field limit high weights is going off the end of the runway about 12 seconds after Vr... so if it takes some time for the trim to reset (say 8 secs), and then some time to rotate (say 5 secs), it is going to be close... really close (yes attitude will start to change at some point as the trim is being run...). The reject is also going off the end, at around 80-100Kts... dealers choice. The light twins are going to be in better shape for both stop and go cases. Individual case will depend on runway available, weight/thrust etc.

Best place to have this is in a sim, and probably not as an unbriefed event. Before placing any faith in the go case on a 4 engine aircraft, would really want to practice that is a sim to assess runway used. While the sim is not necessarily certified for that evolution, the trim response "should" be close to representative.

The above is some background on the issue, and should not be construed to be a procedure. At the end of the day, the buck stops in the LHS.:=

Good luck!:)

BarbiesBoyfriend
25th Feb 2010, 23:57
Has anyone ever had a jammed elevator on take off, in a 737?

Worry about more relevant stuff, if you must worry.

Sciolistes
26th Feb 2010, 01:06
Hi yankee, if the control surface wont move then neither will the control wheel - at any speed.

glhcarl
26th Feb 2010, 01:27
Hi yankee, if the control surface wont move then neither will the control wheel - at any speed.


What type of aircraft? On the L-1011 if an aileron is jammed, bungees installed in the input system will extend or collapse to allow movement of the control wheel and any un-jammed aileron. Even if all four ailerons were jammed the wheel will still move, but it wouldn't do you a lot of good.

411A
26th Feb 2010, 03:37
Even if all four ailerons were jammed the wheel will still move, but it wouldn't do you a lot of good.

Then again, it might...if any flaps/slats are extended, due differential spoiler actuation with control wheel movement.
L1011, a superior design:}

john_tullamarine
26th Feb 2010, 12:37
The aircraft was dynamically unstable, but only mildly so

Probably not ? In general, a knowledgeable pilot (read TP training) might manage to fly a circuit in a statically unstable aircraft but it would be a bit of an ask to expect a successful outcome in a dynamically unstable example.

The tale is a thing of eyebrow raising and heart thumping ... and excessive sweating.

glhcarl
26th Feb 2010, 17:50
Then again, it might...if any flaps/slats are extended, due differential spoiler actuation with control wheel movement.

I don't think so. The L-1011's inboard spoiler mixers and outboard spoiler selectors are driven by the inboard aileron feed backrods. Therefore there can be no spoiler movement if there is no aileron movement. So even with the flaps down and the mixers and selectors set to deploy spoilers 2 through 6 on the up aileron wing it will not happen if the aileron does not move.

Sciolistes
27th Feb 2010, 01:20
Carl,
What type of aircraft?
737 of course :)
On the L-1011 if an aileron is jammed, bungees installed in the input system will extend or collapse to allow movement of the control wheel and any un-jammed aileron.
The answer was in the context of the elevator. But on the 737 the Capt's control wheel controls the ailerons and the FO's the spoilers. Both control wheels are connected thus actuating both types of flight controls accordingly. If a jam on either side is experienced, the opposite side can break the connection and have some roll control.

411A
27th Feb 2010, 02:08
If a jam on either side is experienced, the opposite side can break the connection and have some roll control.

On the L1011, the handle labeled 'pull roll disconnect' will accomplish the same purpose.

Denti
27th Feb 2010, 07:35
Scratching at fading memories here but isn't the range of the main electric trim on the 737 less than the full range of manual trim wheel inputs, hence full nose down trim will be unrecoverable without manual trim wheel input?

Actually, depends on flap setting, if flaps are in a different position than 0 we can use fast speed electric main trim for nearly the whole trim range (forward limit is 0.4 units), if flaps are 0 forward trim range is limited. Even if manually set full forward you can allways use the electric main trim to trim backwards.

Port Strobe
27th Feb 2010, 12:42
Denti & KG

Thanks for that, makes sense that MET would be allowed to get you out that corner. Taking the flap lever out the UP detent was mighty useful to set full AND trim prior to deicing :ok:

glhcarl
27th Feb 2010, 17:50
On the L1011, the handle labeled 'pull roll disconnect' will accomplish the same purpose.


411A, if you want to have a little fun, pull that "roll disconnect handle", then have your co-pilot turn his control wheel full left, at the same time you turn your control wheel full right. All 4 ailerons will move full up. :)

Now, lower the flaps to 4 degrees or more, and do the same procedure above. Now along with the 4 full up ailerons you will get 12 up spoilers, for even more fun.:D

Both of the above may be a little to much fun to have while you are in the air, so I suggest they only be accomplished on the ground.:ok:

411A
27th Feb 2010, 20:44
411A, if you want to have a little fun, pull that "roll disconnect handle", then have your co-pilot turn his control wheel full left, at the same time you turn your control wheel full right. All 4 ailerons will move full up.

Now, lower the flaps to 4 degrees or more, and do the same procedure above. Now along with the 4 full up ailerons you will get 12 up spoilers, for even more fun.

Both of the above may be a little to much fun to have while you are in the air, so I suggest they only be accomplished on the ground.

Noted, with thanks, glhcarl...we have some new guys in training so it should be....informative, to say the least....on the ground.:}
We do most of our pilot/FE proficiency checks in the airplane now, since the Bournmouth L10 sim went TU some time ago.

Recall years ago some DC8 pilots were in training on the L10, and they tried some pre-start control checks, with hydraulics...OFF.
Aileron crosshatch lights illuminated, as you might expect, and I was called from hotac at 3am...and asked...'whatever could be wrong?'

My simple reply...'RTFB, dummy, it ain't a Douglas.'