View Full Version : B757 Flap/slat Non-normals

24th Jun 2002, 15:00
Could anyone help me with a discussion on a company B757 sim senario? During take-off a tyre on the left main gear blows. The gear and flap is raised normally. Subsequently, during the appoach, the aircraft suffers a flap/hydraulic problem that prevents the leading edge slats from deploying. Additionally the left main gear will not lower and so a landing on one main gear and the nose gear is required.

When dealing with the LE slat problem, the QRH says to deploy the trailing edge flaps on the alternate system to 20degrees only. My understanding of the reason for this is that it will provide sufficient go-around performance should this be necessary (the alternate flaps are very slow to operate).

However, clearly one would want to land at the slowest possible speed with one main gear retracted. To deal with the gear problem it would be better to land with full flap (30 degrees).

My question is this: Does anyone know of any aerodynamic reason or any other reason (other than G/A performance) why a landing with 30degrees of flap and with no leading edge slat should not be attempted?

24th Jun 2002, 20:23
A dilemma we have. One Non-Normal checklist says to use flap 20 for landing (LE) and the other to use flap 30 for landing (Gear up). However as I am paging through my QRH I see no reference to LE up and TE 30. Therefore I have no Vref speed for final approach if I use TE 30, the only reference I have for LE not in extended position is TE 20 and Vref 30 + 30 for landing.

However I have had simular problem in the Sweatbox you are describing, but there was only hydraulic problem and we extended both the LE and TE flaps on the alternate system even though the checklist said only to use flap 20; this was done, like in your problem, because we had one gear up and wanted to land as slow as we could. We got no comment's from the allseeing god, that sat behind us :p

In my view: Use flap 30 for landing if having gear problem, even though one has to use alternate flaps.
If no LE, use flap 20 and Vref 30 + 30 as QRH says as we have no other speed reference in our books.

25th Jun 2002, 02:08
Flap 20 for your go-around performance, Flap 30 for landing performance. Your decision now is which one do you need more. Flat terrain at the other end of the runway means that you won't require the full go-around performance, big hill at the end of the runway and you may decide that the extra 10 or so knots on landing is worth it to preserve that go-around performance,

25th Jun 2002, 19:51
IMHO... If the figures for the flap30 LE retracted are not published do not do it, if Boeing wanted you to use this configeration they would have supplied the speed, at the subsequent enquiry you would be crucified for makeing up your own speed, also what speed would you use?
Only one gear leg has failed to lock down, two are down and locked, therefore cannot use 30flap/LE retracted as Boeing does not cover this as a landing config. or supply these speeds.
I feel the flying and threshold speed for the flap/Le config. has priority. There is no need to improvise outside of the QRH in this case as it is covered by what they left out.
I thought multiple failures were nolonger allowed in the simulator anyway and you could have aborted before V1 for a burst tyre.
I found abandoning with tyre failures on one side, be prepared to use the nosewheel tiller positively (or call for its use if not fitted your side) as you run out of rudder pedal steering and directional control to stay on the runway centerline.

Cornish Jack
26th Jun 2002, 12:08
This is outside my normal operating sphere (Type-wise). Have any of you posters seen the A A L training videos dealing with CFIT, Control Malfunctions etc?
The significance is that the presenter - an A A L training Capt of some considerable experience - uses an almost throw-away example of control malfunction quoting 757 flap assymetry (inboard) as an example of uncontrollable roll input. He described the effect as so dramatic that, initially, his flight sim instructor teams deleted the fault from the simulator because they considered it to be IMPOSSIBLE to deal with!! Subsequently, some eight(?) years later they re-introduced it as part of the package of training measures incorporated to deal with 'crossover' speeds - NOT just for the 737 rudder problems. Could this have something to do with the limiting flap input as well as the other reasons?

26th Jun 2002, 14:03

careful here. I think you would be considered unwise to abort for a tyre failure prior to V1. Prior to 80 knots fine, as stated in my Boeing QRH (NNM1.1), but prior to V1 is a little more dodgy. Boeing (NNM 1.1 again) say above 80 kts reject for engine failure; fire; or, if the airplane is unsafe or unable to fly. The Boeing video on RTOs specifically says NOT to abort for a tyre failure above 80 kts (I accept that other things may cause damage that might requiire an abort). However, you are 'off-piste' if you do abort. Exactly at the moment when you need all the braking available to stop in the available field length you have reduced braking because a tyre is not available - you may be answering the questions from the overrun/ditch!

Now reading between the lines I suspect the guy driving the console was implying that if you had left the gear down, checked with the tower whether a tyre had burst on the runway or not, and then returned to land, most of the problems would not have occured (presumably your 'god' has considered broken tyre whizzing around the gear bay may cause some hyd lines to rupture with odd consequences).

Now, if you are stuck in that situation I can agree with everybody!(flaps best set for min speed if GA not a problem, but what speed would you use, and should we really be making the speeds up?).

However, you are not in a rush. Does anybody know if Boeing provide a service on HF or for your ops to call to get more advice in such circumstances?



Old Aero Guy
26th Jun 2002, 20:50
As has been noted earlier, no approach speed is published to a No Slat, Flaps 30 configuration. No procedure for a specific configuration usually means it's one that should be avoided. In this case, there are probably two reasons, both related to having a deployable leading edge device.

1) A deployable leading edge device allows the clean wing airfoil to be optimized for cruise. Using a steep flap deflection like Flaps 30 without the leading edge device extended for such a wing could result in a configuration that would have an abrupt leading edge stall and very nasty stall characteristics which would be difficult to sell to the certifying authorities.

2) A deployed leading edge device lowers stall speed by increasing stall angle of attack. If the leading edge is not deployed, the stall angle of attack at Flaps 30 may be so low that the corresponding operating speed to provide adequate manuever capability (even lower angle of attack) may make it difficult to land without having the nose gear touchdown before the main gear. Nose gears are not designed for this type of abuse.

27th Jun 2002, 23:34
av8er Thank you for picking up on that point.
I did not see the Boeing RTO video despite operateing the 767-300er for 11years. I stand corrected.
I was taught if one tyre went on a heavy jet 4 tyre truck, its axle mate would overload and go seconds later, you listened out for the double pop, got hydraulic warnings from the damage and aborted. So for me it was one pop after 80kts go and two pops stop.
Hydraulic and leading edge damage is unlikely to leave an engine or engines undamaged.
To continue would leave you possibly unable to retract the gear with hydraulics gone and parts of the damaged tyres likely to be ingested into the engines, flap/slat/hull damage etc.
If this tyre burst was on a max heavyweight takeoff I felt the 767 aircraft was unlikely to fly on one engine with gear down and with possibly two hydraulic systems out.
Prevoiusly my airline operated L1011 and had a great deal of tyre problems and some aborts in 1975/6.
With a tyre failure, a Ba Captain at Cdg attempted to continue as he was taught at BA, the axle mate failed, the boggie draged, the takeoff then had to be aborted as the aircraft would not accelerate. The remaining two tyres failed, the bogie was destroyed and the gear leg ploughed the runway, that helped it stop.
The same thing happened (tyre and axle mate tyre failed) on takeoff in Karachi, but this Captain based on the Cdg incident immediately aborted and useing tiller steering kept it on the runway with much less damage than the Cdg incident.
We were required to demonstrate on the 767 remaining on the runway aided by the tiller steering with an axle double tyre failure based on the companies experience of these L1011 tyre abort incidents.
However I accept that Boeing has considered all this and it is unimportant if the axle mate fails or not, the hydraulics and engines could be damaged but this is acceptable, and that today the method they require taught, is to once again as the Ba Captain was taught to take the tyre failure/s and hydraulic failure/s into the air after 80kts.
Today Boeing must know you can still accelerate and control it to Vr with or without the axle mate tyre failing and all of the above so its nolonger a non normal... until you rotate?
If you do not return safely you can always complain to Boeing. They will explain that as the aircraft has now been proven unflyable you should have aborted/abandoned.
Do you recall the Spanish Captain in a DC10 who did a very late(20 ft airborne) rejection and the Cdg Concorde both results were not good but one was much better than the other.
The lesser of two evils and a difficult call.
I am very glad I nolonger have to consider the legal implications of this call one advantage of having been terminated by the age 60 rule.