View Full Version : 737 tech probl...
28th Mar 2007, 13:07
Hi guy.... what do you think about this kind of problems?
1)@<hidden> 80 kts you have 2 different ias reading...do you continue the take off' and when on flight...do you continue to the destination'
2)Afer take off is it possible to retract the Leading Edge device when you have loss of sys B? ( I mean with PTU...)
3)on take off......eng failure...just after lift off and gear up...wheel well fire..... Do you estend immidiatly the gear or you'll wait antil msa?
28th Mar 2007, 15:20
1. @<hidden> 80kts it would be a good idea to reject the Takeoff. That is one of the purposes of the 80kts call. ie to cross check the ias. I would reject below 80kts for any master caution.
2. The PTU uses system A pressure to power an hydralic motor driven pump to pressurise system B for auto slat and leading edge device operation. It automatically starts when these 3 conditions exist simultaneously: Airborne, system B engine driven pump pressure drops below a limit and the flaps are 15 or less but not up.
so the answer is Yes as long as you still have enough system B fluid.
3. Boeing doesn't make consideration for 2 failures at the same time. ie because of there low statistical probability of occuring. ie engine failure while wheel well fire is pretty unlikely so u won't find a NNC in the QRH combining the both. if they did that the Q(uick)R(eference)H(andbook) will become the L(ong)R(eference)H(andbook) :)
that is why the CRM and decision making is so important. The commander must assess the situation and decide the best course of action.. there are many factors that must be considered. eg if in VMC and terrain clearance is assured and the engine performance is sufficient to overcome the extra drag of the gear and a suitable airport is in close range .. I don't see why u would wait until MSA to extend the Gear.
28th Mar 2007, 15:23
1. 80 kts -different IAS : REJECT . No way you'll want to take off with unreliable speed, you'll set yourself for some problems. People did crash due to unreliable speed,more than once.
I've participated to a Boeing Flight Safety symposium and they were very clear:reject.In case of unreliable speed in the air one important thing they told us was the importance of having visual conditions when landing.
This was proven by statistics,no major problem was when unreliable speed occured and the flight was continued in VMC till landing. Most problems where at night or during IMC.
2. I think you should read again the description of the PTU. The PTU is providing a backup pressure from sys A if sys B eng driven pump pressure drops in order to provide power for AUTOSLAT operation. This means enhacing stall characteristics at high AOA ,when LE are in MID position (TE pos 1-5).The LE automatically drive to full extended position when approaching stall,and after AOA is decreased the LE go back to mid position.
In case of sys B failure the LE will remain in position they were at sys failure.Thus the IAS limit.
3. What would you chose : risking the fire in wheel well area or hitting the hill ahead. Personally I'll keep the gear up if terrain is a risk.
The Ng will present a problem though,as in case of wheel damage the gear won't retract,to prevent further damage. If then will follow one engine failure,well..:mad:
You should know the airport area, where are the most important obstacles.
You have a nasty sim instructor,don't you?:hmm:
29th Mar 2007, 14:40
80 kts you have 2 different ias reading...do you continue the take off'
It depends on the accuracy of the observation and when the call was made. Generally and we see this a lot in the simulator, the PNF calls 80 knots when in fact he has called after the aircraft has passed 80 knots and the PF's IAS might now be reading 90 knots. At the 80 knot call you should be cognisant of the ground speed reading and a really serious IAS spread between the two or three ASI's is quickly sorted out. Don't take ANY abort lightly. If the PNF has not called 80 knots when the PF sees his own ASI going through 80 knots then the PF should call his own speed - eg "87 knots my side" which should be enough to galvanise the PNF into calling a similar speed in response. Often we see the PNF still fiddling with thrust levers to set N1 as the IAS flashes past 80 knots and he misses reading his own airspeed indicator until too late for accuracy check between the two ASI's.
29th Apr 2007, 08:58
The purpose of the PTU is to supply additional volume of hydraulic fluid needed to operate the autoslats and leading edge flps and slats at the normal rate then system B engine - driven hydraulic pump volume is lost. The PTU used system A pressure to power a hydraulic motor-driven pump,which pressurizes system B hydraulic fluid. The PTU operates automatically when ALL of the following conditions exist :
1. system B engine-driven pump hydraulic pressure drops below limits
3.flaps are less than 15 but not up.
(c) Incase of a wheel well fire, extending the landing gear is incorrect since a wheel well fire is not a recall item. Depending on company procedures there should be a minimum altitude at which the crew is allowed to commence non-normal checklists.
Often we see the PNF still fiddling with thrust levers to set N1 - not 'often' on my flight deck! If they are, I encourage them to:-
a) stop doing it
b) read the Boeing article on the setting of take-off power by the autothrottle system.:)
29th Apr 2007, 14:03
If for some reason the autothrottle didn't manage to set Takeoff Thrust correctly until 82kts you have to fiddle to set it since then the autothrottle is in HOLD mode, at least on the classics. Happens more often than not especially on older aircraft. Another often seen thing is the hanging behind or lagging of one thrustlever servo so that you get quite a big imbalance in set thrust, not something you want to see so fiddling again can solve that problem.
29th Apr 2007, 14:20
Denti , as I remenber, the thrust should be set by 60 kts. the a/t will manage that,with a error of +/- 2% N1 after THR HLD. This error can be then corrected by the PM ,if required , to -0/+1% N1.
So,normal order is :
engine stabilized,push toga ,thrust set by 60 kts with a possible momentary 4% N1 overshoot , ...followed by 80 kt call, then at 84kt THR HLD on the FMA , followed by eventual manual thrust correction to -0/+1 % N1.
No need for the PM to miss the '80kt' call while fiddling with thrust levers-this should be done after 80kt.
1) As Centaurus has pointed out, missing an exact 80 kts call can happen, not often, as BOAC says, but still happens from time to time for various reasons (strong headwinds or whatever...).
I would tend to continue my takeoff, because of:
A) the redundancy in airspeed indicators: four main ones, one standby, four GS...
B) as David Davies said, knowing the relation between pitch, power, speed and so on, will give you enormous confidence in flying your airplane.
if you are a pilot, you are not gonna crash like the ****** Birgenair three (!) ***** in their 757 :mad:
2) if B fluid is still there and for some reason you loose both pumps (loss of B in your scenario), yes you can retract the leading edge thanks to the PTU.
As this operates with flaps less than 15, you can use alternate electric system to raise the trailing edge flaps if taking off with F15, than le LE with the PTU.
3) asking this kind of questions is the difference between a Captain and a copilot looking for simplistic rules to apply anytime.
Another 3000 stecks and you'll know the answer my friend!
11th May 2007, 22:44
80 knots is a reasonableness crosscheck. If missed I would expect the suport pilot to call 85 or 90. We dont have any published acceptable splits so back to reasonablness. At this point of acceleration I guess 20 but I will read the manuals to see what inflight split would generate messages on a 800. As for the gear well fire and engine failure. Go back to basics. control performance procedures. Hands and feet then are we climbing? Remember that if you are on a published departure that they are predicated on achieving a 3.3% climb gradient to remain clear of terrain and within controlled airspace.Any increase above this figure isnoted on the chart. Your second segment engine out performance is 2.4% gear up and engine out. So at about 150 knots if you have in excess of 495 feet per minute (3.3% means 3.3 x groundspeed) then terrain is not a problem so how much excess can you trade off for the drag associated with a wheel well fire? By the time you have thought about the fact that you don't know because you don't have any figures you will find yourself at 1000 agl and then in a position where you would clean up the flaps at near level flight. So if the terrain would allow you to clean up at near 0% gradient then put the gear down and return for an approach. WE circle engine out at Flaps 10 and put the gear down on base turn or g/s alive. That is to leave a thrust margin over the drag associated with the gear. If you have left the flaps at 5 from the takeoff and are flying gear down because of the wheel well fire then take the flaps later.That is when you get to procedures. Today a wheel well fire is not a recall checklist as per many others that once were however , the pilot in command may direct checklist procedures to be accomplished be recall under certain conditions. Someone chipped you that if you are asking then you aren't ready to be a captain. Nonsense. If you are asking because you wish to have a prescribed response to all scenarios then that indicates a lack of aviating maturity. If you are trying to develop a pattern of thinking that you can overlay most scnarios and arrive at a safe conclusion then you are well on the track to becoming a captain.
12th May 2007, 04:24
IAS discrepancy at 80 KIAS.
As craig freier has said this is a "reasonableness", check. The Boeing FCTM confirms this, and goes on to say "that if there are any questions, another source of speed information is the ground speed indication." You might also want to check and the compare the standby ASI.
On the NGs the ASI Disagree alert (Amber) will annunciate when the difference between the Capts and the F/Os ASI disagree by more then 5 Kts for 5 continuous seconds. Being an amber caution, that doesn't come with a Master Caution, is this Boeing's way of saying do not abort?
Retraction of the leading edge flaps and slats after the loss of System B Hydraulics (via the PTU).
The QRH drill for loss of system B Hydraulics warns you at the end that "the drag penalty with the LE devices extended may make it impossible to reach an alternate airfield". I confess that I thought the PTU was limited to moving the slats from extend to full extend and back again, but I could be wrong!
Engine failure, followed by a wheel well fire.
Neither drill is now a recall drill so both should be left to, typically, 1000' AAL. Now you need to prioritise. Which one is likely to kill you sooner! If you have taken off over open sea, on a lovely summer afternoon, then terrain is unlikely to be an issue and I would definitely be doing the wheel well fire drill first and then the engine failure drill. On the other hand if it is at night with a low cloud base, and terrain is an issue, then I would probably delay carrying out the wheel well fire drill until I was above MSA, arguing that whereas delaying initiating a fire drill may kill me, hitting a hill top will definitely kill me.
Just my 2 cents!
14th May 2007, 02:22
the wheel well fire checklist does not contain recall items but the "checklist introduction" section of the QRH says that reference items can be carried out from memory at the discretion of the captain...I would personally extend the gear if I had a wheel well fire, unless climb performance was seriously compromised, after an acceptable safe altitude. You never know how serious a fire in the wheel well can be...there flight control cables, hyd pumps, reservoirs in there...I ´m sure it´s all fire resistant to a point, but a fire not rapidly extinguished could put me in a manual reversion scenario later"
apu fire...i wouldn´t wait for someone to pull a checklist out of a bag, I´d do it by heart...more examples? starter auto cut out failure...tailpipe fire...I am not suggesting rushing thru a procedure, but identifying the problem and proceeding logically to prevent a bigger problem later...
16th May 2007, 06:11
The PTU will only operate the L.E. flaps from extend to full extend and back to extend again under the conditions that some of you have posted here. That is, loss of system 'B' Pressure, aeroplane in the air and flaps at 1, 2 or 5.
It does it by rerouting 'extend' pressure to the 'full extend' port. It will only do this if there is a stall and the SMC/SMYD commands it.
There has to be pressure in the extend line (ie the LE flaps have to already be extended).Also, in this condition only the SMC/SMYD can command the LE flaps back to 'extend', and only as far as 'extend', not fully retracted (when the stall condition no longer exists).
You could be confusing PTU operation with the 'Alternate Flap' operation, however, that will only extend the L.E. devices to full extend, with no intermediate positioning of the L.E.flaps. It will not retract them.
You cannot operate the PTU without system 'B' fluid, (well you can, but it won't have any fluid to act on) however, loss of system 'B' fluid does not necessarily mean loss of standby system (alternate L.E. flap extension) fluid operation.
It should be noted that once the Alternate flap switch is armed, this will deactivate the P.T.U.
I am reading this right now from my engineering notes from both the 737-3/4/500 and 6/7/8/900.
To summarise, you cannot retract the L.E. devices with either the PTU or Alternate flap on the 737. You must have the normal system 'B' operating.
frits van thiel
12th Jan 2010, 19:12
The purpose of the PTU is to provide automatic back-up power for the slats to move from extend to full extend if the EDP in the B system has a low reading, the flap handle is in “ not up” or further than 10 units and the aircraft is in the air. The pressure is used if an auto slat command is given.
So in summary;
The PTU control valve supplies A pressure to the motor side of the PTU if all these conditions are met:
· The aircraft is in the air,
· Flaps not up or further than 10 units, (flaps are in the extend)
· The pressure from the EDP in the B system is 2350 psi or lower for > 0.5 sec.
If the pressure from the EDP B is returning to values above 2350 psi it will not close the PTU control valve since it is latched after 0.5 sec.
The PTU pressure cannot be used for retraction of the slats since the flap handle is than selected in up, which make the PTU to stop. (see the conditions above)
The Landing Gear Transfer Valve has nothing to do with the PTU system. Altough it has to be mentioned that this valve will be closed if an auto slat command is given simultaneously
with a PTU control valve open signal, the LGTV will be closed to reduce the power drop during the landing gear up selection in the “A”system. A pressure drop in the “A” system affects the speed of the PTU motor and so the output.
frits, technical instructor 737.
12th Jan 2010, 19:38
Flaps not up or further than 10 units, (flaps are in the extend)
Is that still correct for the 737NG with SPF? IIRC the SPF mod changes the leading edge device schedule and they stay in the extend position until flaps 25 and autoslat function is available between 1 and 25 as well.
12th Jan 2010, 19:59
The PTU function and schedule is unchanged for SPF aircraft, even though as you say autoslat is available through to 25 for these a/c.
12th Jan 2010, 20:20
Thanks for the info, allways a pleasure to learn something new here :)
14th Jan 2010, 03:12
At my airline the 80kts call is also an incapacitation check.
Is this briefed in any of your airlines? Just enquiring for interests sake. Framer
14th Jan 2010, 03:43
Yes the one I fly for, includes incapacitation check, BTW from what IAS value the master caution is inhibited during Takeoff?
14th Jan 2010, 07:37
Yup, incapacitation check and speed crosscheck in one here too. The 737 does not have a mastercaution inhibition feature, only some warnings are inhibited from 80kts on (like the low oil pressure lower DU popup).
15th Jan 2010, 01:16
just a minor correction to the post by alexban...
he said, I quote:
"The Ng will present a problem though,as in case of wheel damage the gear won't retract,to prevent further damage."
that may be read out of context here...
What he meant was:
"The Ng will present a problem though, as in case of MLG wheel damage, that particular gear won't retract, to prevent further damage."
Just thought I'd make the distinction!