B737 Maximum Flaps Extended Altitude

[john_tullamarine]

Aterpster,

My admonition probably wasn't directed at your good self ...

Chaps,

The limit is a certification matter and has been done to death in previous threads on the subject. One of many is this one. I note that MFS plays with this stuff day in day out in his day job ....

In addition,

(a) there are certification discontinuities at 20,000 feet

(b) the structural load capability with flaps is reduced compared to clean

in the Standards.

The real killer is that there is no obligation on the OEM to investigate high altitude operation with flaps. Unless the AFM indicates a permission to so operate, a general limitation is prescriptive. Bush lawyering is not useful when interpreting AFM matters.

In many respects there are things which are not explicity proscribed in aviation and this is one of them.

Consider what one's story might be at the Inquiry after the mishap should one have elected to play test pilot with someone else's aeroplane ...

Will be having dinner with MFS in a day or so, so will ask him his thoughts on the matter.

[BOAC]

Whilst I hope you enjoy your dinner, JT, you might wish to read MFS's contribution in your link at post #6 and I-2021 at post#9 in http://www.pprune.org/tech-log/27870...e-20000-a.html where 300kts /0.65M would seem to be an absolute limit, and to lay the 'you're going to be a test pilot/die in flames' rubbish to rest, Checkboard at post #37 here.

BtS - as I said before, there is no answer the way Boeing have worded it. Hope you have some food for thought from the more 'thinking' contributors here. If some day you are in charge and you need to do it for whatever reason, it is your decision. (and ignore reference to TAS, by the way.'Tis IAS wot breaks things and Mach which causes control issues basically.)

As proven,

Once again proof there are stupid answers.

[vilas]

Breakthesilence is asking legal interpretation of flap extension. He is not interested in theory of DOs and Donts. If Boeing permitted extended flaps beyond 20000 they would have said so. In absence of that it simply means flaps have to be up beyond 20000ft. Line pilot is not expected to find solutions when manufacturer has not provided them. According to me it is not permitted you need to land back.

[nitpicker330]

I'm not confused about anything chaps.

Lets assume VFE of 240 kts at FL200. Around 320 kts TAS.
VFE of 240 kts at FL380 equals about 450 TAS.

A much higher TAS and therefore Airload on the devices.

Naturally you'd have to be close to VFE during cruise at FL380 otherwise you'd be below Minimum Speed. ( in most heavy jets anyway )

That's all.

[BOAC]

OK nitpicker - your starter for 10-:

The International Space Station has a TAS of 17,239mph in orbit, but an IAS of practically zero. What are the air loads on the assembly? If it had 'flaps' and extended them, would they be ripped off because of the TAS?

[john_tullamarine]

and to lay the 'you're going to be a test pilot/die in flames' rubbish to rest

Good sir, I have a conservative view of life (boring old engineer and all) .. which gets more so as I get older, more doddery and less desirous of dying.

TPs get to have lots of boredom (for which the sensible ones strive) and the occasionally interspersed moments of terror (when something happens which they didn't expect) .. to let us mere mortals have an easier time of it and get all the excitement we need in the bar on overnights.

Rest assured that the topic is bound to be a dinner topic.

You cite Checkboard .. I quite liked his summation ... "Flaps aren't tested in this region - here be dragons". It's a bit like the old QA audit axiom .. "absence of evidence is not evidence of absence".

[BOAC]

get all the excitement we need in the bar on overnights

- so - the rumours are true?....................

[john_tullamarine]

.. indeed ... I can recall waking up the next morning in some of the more highly regarded bars in places here and there ....

Ah, memories .. now, I'm on the slippery, slidey slope to Hell as a consequence.

[BOAC]

Let me give you one example of where I once flirted with death, and chose to leave the comfort of "all the excitement we need in the bar on overnights.", devil that I am.

I once (late 80's) took delivery of a Cessna 310R (on the British register) to be operated on my AOC in Scotland. A nice ship - fully booted, electric window and prop de-ice etc BUT the CofA said "Not cleared for flight in known or forecast icing". The type fully 'iced' in the US. I asked for the restriction to be changed - no.

Why? The necessary 'icing trials' on the 310R to satisfy good old Auntie had not been carried out. Now, my problem was, and I don't think it has changed, that icing was 'forecast' EVERY day in the Scottish FIR - a bit of a problem, really. My then Flt Ops inspector was one of the early sufferers from 'restricted timber vision' (wood and trees etc - I have other stories............) and I just KNEW my AOC, if not my ATPL, would be in peril at his next 'regular' inspection of minutiae. So, I gently enquired the cost of the 'icing trials' - and fainted. After significant to-ing and fro-ing (and those who have tried to run small AOCs will know what I mean), I FINALLY got the restriction changed to '"No flight in Known Icing conditions" (hoorah!)

You will never guess what I used to do on my flights, will you? - and I didn't crash or burn. Yes - I flew that aircraft in uncharted territory, and THAT was a restriction that was abundantly clear in its intent (and wording) too.

[Turbine D]

This discussion is very intriguing to me as an engineer. Here is a photo of the Boeing 737 Classic triple slotted TE flap extended.


Triple slotted trailing edge flaps at the 40 position on a 737-400.

Now true enough, Boeing says not to extend the flaps above 20K feet as they never certified the aircraft in this configuration. I suspect they do know some things from a design analysis/stress point of view as to why this isn't a good idea, but never confirmed it in flight testing/certifying the Classic, and just said don't do it.
However, the story may be different in the Boeing 737-NG series. Here the flaps are double slotted, not triple slotted. And Boeing says this:

Although the flap placard limit speeds are different for each 737NG variant, the structural limit speed for the flaps is equal to the placard speeds (175k – F30, 162k – F40) for the heaviest variant (737-800/900). The Flap Load Relief trigger speeds (176k – F30, 163k – F40) are set to allow all variants to fly to the structural limit speed without system activation. Setting lower flap placard speeds for the –600 and –700 variants allows for greater service life of flap components due to the larger margins to the structural design speed.

For the NGs, speed is important, can you cruise and maintain level flight above 20,000 feet at less than 200k, 176k or 163k?

Going back to the Boeing Classic, Boeing says:

A flap load limiter (-3/4/500) / flaps/slats electronics unit (-NG) will automatically retract the flaps from 40 to 30 (-3/4/500) / also 30 to 25 (-NG) if the limit speed is exceeded. The flaps will extend again when speed is reduced.

At this point, I am assuming there to be an automatic sequencing of leading devises ( 2 Kruger flaps inboard of each engine) and 6 slats outboard of the engine per wing. So extending the TE flaps, these devises extend first, correct? If so, I wonder if there are stress limits determined by speed for these, more so than the TE flaps? Any thoughts, any one?

[galaxy flyer]

I'd add that with the LEDs extended the flow over the wing might be accelerated beyond Mach 1, which would add the the stress on both sets of high lift devices.

[zxccxz]

Guys: not an emergency, but the flight was continued..

Report on the low fuel incident of KL874, a Boeing 747-406, PH-BFC, en route from Bombay (VABB) to Amsterdam (EHAM), on 14 July 1994


Operator: KLM - Royal Dutch Airlines - Aircraft type: Boeing 747-406 Combi Registration: PH-BFC Flight: KL874, scheduled from Bombay Airport (VABB) to Amsterdam Schiphol Airport (EHAM) Date: 14 July 1994 Place: During descent into EHAM


Synopsis
After an uneventful take-off from Bombay Airport in heavy rain, the EICAS alerts "Flaps Primary" followed by "Flaps Drive" were triggered during climb, passing FL220, at an airspeed of approximately 330 kts. The respective emergency checklist procedure was performed and after some delay, due to poor HF communications, clearance was obtained from Bombay ATC to descend to FL200, in accordance with the emergency checklist procedure. KLM movement control and KLM maintenance support were contacted via HF radio and in concert with KLM maintenance support the flaps were recycled between positions 'up' and 5 several times, by use of all available operating modes. However the flap warning persisted and it could also not visually be verified that the leading edge flaps were fully retracted. It was decided that the flight could continue but that the respective flaps 5 limit speed should be observed. However in concert with KLM operational engineering, it was decided that the stated altitude restriction was not applicable and that the aircraft could climb, given the normal operational envelope and the additional speed limitation. An intermediate landing at Dubai was considered, but at that time the aircraft was still operating above its maximum landing weight. Fuel calculations indicated that the flight could proceed to Athens with 25.000 kg fuel remaining upon arrival. While the flight continued, it became apparent that it was also possible to continue the flight to Frankfurt. KLM movement control was informed and a technical team with spare parts was put on standby to proceed to Frankfurt as soon as the final decision was made to make an intermediate landing at Frankfurt. While the flight continued, fuel calculations indicated that KL874 might continue to Amsterdam with approximately 4000 kg fuel remaining upon arrival. Shortly before passing abeam Frankfurt, fuel calculations indicated slightly more than 30 minutes reserve fuel remaining upon arrival in Amsterdam and after consult (via KLM movement control) with the Schiphol Meteorological Office, Air Traffic Control and the chief pilot, it was decided to continue the flight to its original destination Amsterdam. After passing Frankfurt, the indicated amount of fuel remaining upon arrival however started to decrease and ATC did not clear KL874 for an unrestricted descent and approach into Schiphol. During descent it became apparent that the aircraft would land with less than 30 minutes reserve fuel. KL874 did not declare an emergency, but ATC was informed of the critical low fuel situation, after which KL874 was cleared direct to Schiphol. Due to a late descent cleararce, an intermediate level off at FL260, diverging radar vectors from ATC and early flap extension, to verify the correct operation of the flaps, the calculated remaining fuel decreased further and after parking at the gate it was noted that there was 2200 kg fuel left.

[john_tullamarine]

Far be it for me to second guess KLM. However, I can see an interesting time of it at the Enquiry had it all turned to custard.

I don't think that the corporate risk management approach necessarily would win hearts in all parts ...

[737Jock]

1994... explains a great deal I reckon.

[JammedStab]

Not too bright planning to continue to AMS with 4 tons remaining. How do I know. Look at their landing fuel. What about ATC delays or a go-around. What will that burn....3 tons. Will the flaps extend properly. FRA has plenty of things to do.

AIRMANSHIP

[737ngpilot]

My AOM...To prevent excessive structural loads from increased Mach at higher altitude, flap extension above 20,000 feet should not be attempted