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B737-800 Flap speeds

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B737-800 Flap speeds

Old 29th May 2007, 20:50
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ERJFO, I'd be intrigued to know what type you fly and who for as I find it hard to believe that neither your manufacturer or company do not publish advice on the matter. I'm assuming that you fly a commercial airliner.
Boeing Flight Crew Training Manual under Flap Usage sub heading Flap Maneuvering Speed Schedule.
"During Flap retraction/extension, selectingthe next flap setting should be initiated when reaching the maneuver speed for the existing flap position."
"The maneuver speed for the existing flap position is indicatd by the numbered flap maneuvering speed bugs."
Thats Boeings viewpoint, I would be amazed if Airbus and other manufacturers did not have a similar standpoint but I do not have the written word to quote on that.
My company SOP amends this slightly by advising that you select the next flap setting, during extension, when within 10 kts of the maneuvre speed for the existing one to avoid unecessary auto-throttle movement. Always assuming you are at a point when you want the net flap setting. We are also permitted to fly the usual ATC speeds when required by them which may be a bit above the maneuvre speed. Boeing elaborate to similar effect later in the FCTM.
I very much agree that we should not play structural engineer that is precisely why its important to know and follow the laid down guidance.
Take Flap 1 on a 737NG. The Maximum Operating Speed is 250 Kts but at Typical Weights clean speed is about 195 Kts. Thats a 55 Kt difference which at 1/2 MVsquared makes a hell of a difference to wear and tear on the flap.
During normal ops anyone trying to operate the flaps significantly outside that advice will be politely told not to with the reasons given at a suitable juncture.
So there you go Manual references, hope that helps
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Old 30th May 2007, 03:52
  #22 (permalink)  
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The limitations are for normal operations, not emergency circumstances

Actually, the limitations are for both ...

The basic structural, handling, performance etc., qualification of the aeroplane is based on limitations as these provide the fence around the paddock.

Fatigue and planned maintenance considerations are based on a presumption as to the way the aeroplane is going to be operated. If the aircraft routinely is operated less conservatively than such presumptions then one anticipates observing an increase in costs associated with routine maintenance activities. Indeed, if one considers structural fatigue, there has been a number of cases of wings falling off in flight as a consequence of this very point ...

One would be VERY wary about, and careful when, exceeding limitations during emergency procedures ... unless you definitely know that, by doing so, you don't create a bigger problem (generally you won't and can't know this) ... and, at the end of the day, the FDR etc., will catch you out at the enquiry ... be very prepared to defend yourself against some searching questions in respect of acts/omissions which might be indefensible at law.
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Old 30th May 2007, 09:52
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My company/type doesn't provide flap selection guidance. If it was provided (like the guidance that exists for you) I would absolutly follow it.

John, in regards to following limitations in an emergancy... I urge to to look at USA FAR 121.557 part (a) states:

"In an emergency situation that requires immediate decision and action the pilot in command may take any action that he considers necessary under the circumstances. In such a case he may deviate from prescribed operations procedures and methods, weather minimums, and this chapter (FAR 121), to the extent required in the interests of safety. "

Based on my interpretation of that law it looks like violating limitations if needed to preserve saftey of flight is anything but indefensible. Infact the above law says the pilot in comand my deviate from the entire section of FAR 121 (all rules governing airline operations).

Loosly translated if you have to you can break every rule in the book to save lives. An example: If the airplane is on fire, I'll exceed a max tailwind and a max landing weight limit to get it on the ground. Remeber, first rule is to fly the airplane. Now to the same extent I'm not going to overspeed the flaps just because I've declared an emergency for somehting unrelated, like a break failure. Remember procedure is all well and good but sometimes (hopefully once in his carrer) the PIC has to earn his pay and make decisions when there isn't time to open the book. I.E. I'm not going to be the guy that dies because he's reading the evacuation checklist when the center fuel take explodes.

Last edited by ERJFO; 30th May 2007 at 10:05.
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Old 30th May 2007, 11:29
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ERJFO, I'm truly amazed ....

Maybe it would be appropriate for either yourself or your company to clarify this point with the manufacturer of your type and to check the fatigue assumptions on the profiles you fly.

TTFN
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Old 30th May 2007, 12:10
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We have maximum flap speeds and minimum manuvering speeds, but we aren't told when to select the flaps. Just not to overspeed them or fly slower than the minimum manuvering speed for the current flap setting.
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Old 31st May 2007, 05:39
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ERJFO,

Guess that we will just have to continue to disagree. Suggest you consult a lawyer at some stage in respect of your regulatory interpretation ... you will/may still be called to justify your actions if you elect to operate outside the requirements .. and, if you can't do that to the satisfaction of the Regulator/Judge/etc (as opposed to your own satisfaction) then you are at some degree of risk ...
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Old 31st May 2007, 10:47
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Wow!!! How this thread has evolved!!!

Well, I will be the first to admit that I am not a lawyer...especially one who specializes in aviation law...nor am I an administrative law judge, nor am I an FAA person, nor am I an NTSB person...

BUT,

The FAR 121 reg quoted above...and there's a Part 91 reg that is similar...is for emergency situations. AND, the NTSB, FAA, administrative law judge, etc. will expect that the pilot's actions (ostensibly as result of an emergency situation...and the declaration of an emergency) will have had to be something that was to directly aid in mitigating the situation.

I'm trying to think of a situation where exceeding the flap speeds would help in an emergency.

An example of a deliberate violation of a regulation is the exceeding of the 250 kt below 10,000 feet rule. You have some guy on board who is about to die of a heart attack, and you're hammering the speed to get the guy to airport "X" where the cardio medics are standing by.

This would be OK, but during the approach, you start hanging the flaps out at Vfe + 10....and that's not OK.

Again, I am NOT a lawyer, judge, FAA guy, or NTSB guy.

Again, I think they would look at your actions, your logic, and how all of this applied to the emergency situation. I really don't think they give you carte blanche....

Just my humble opinion. No disrespect intended to those who disagree. I could be, very well, totally wrong. (I am much of the time!!!)


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Old 31st May 2007, 14:13
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John,

Thats fine with me. I'm just reading the rules from the book. I do have one question for you - Are you saying in absolutly no circumstance is it ever okay to violate a limitation or regulation? What is it exactly about my post you disagree with?
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Old 31st May 2007, 15:26
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Emergencies are very different from ops normal. What I will say is that things will need to be getting rather extreme before you'll find me busting airframe limits. One thing is for sure, if it gets to that point you will be justifying your actions to people who will pore over the detail second by second and in minute detail. If its me and something like that has happened I'd just be glad to be alive.

ERJFO if your company does not publish the advice then I would suggest you use common sense. Push the limits plane breaks sooner, fly conservatively plane lasts longer. Simple stuff. On the other hand if you disagree why don't you drive YOUR car continuously at max revs, slam the brakes, power slide round corners etc being carefull to keep just inside the manufacturers limits. Of course that would be dum though wouldn't it as it would cost YOU money and most probably penalty points or your license. Treat your companies aircraft poorly and it will cost them money and by default you as well. To operate to the limits against common sense to me smacks of a certain degree of stubborness.

If your still struggling write to your manufacturer and ask their advice.

Last edited by Ashling; 31st May 2007 at 15:40.
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Old 1st Jun 2007, 08:42
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Yep!!!

Ashling,

You speak with great wisdom!!! Yep, the airplane is our jobs. The longer it lasts, the better off we are. The cheaper it operates, the better off we are.

I used to try to explain to the 'new guys' this way:

Our company manufactures widgets. We have a big plant, and in it are many widget machines. These machines are expensive to purchase, expensive to maintain, and finicky to operate.

And, the widgets, thenselves, sell for a price only pennies above the cost to produce. So, we have to crank out as many as possible in any given day. (Hence, good aircraft utilization with good load factors.)

It's important that we, the widget machine operators, treat the machine with kid gloves. We know better than anyone how to baby the machine, to make it last, to make it produce the most widgets in a work shift, in a machine's lifetime.

If we fill in all the above squares, the bean counters will be pleasantly surprised...and will happily replace the widget machine when its life has expired...and gladly train the operator on the new state-of-the-art widget machine that replaces the old one.

And, the bean counters will buy more widget machines...and cram them into the factory building, since these machines make a profit for the firm...and they'll hire and train new operators to operate these machines...and you'll gain seniority...and more pay and benefits...and vacation, etc., and job security.

So, it's important to save 30 seconds of flight time by going to the trouble of asking ATC for 'direct' or doing a slow-speed, thrust-idle descent...using your skill and experience to plan the descent so you don't touch the thrust until 1000 feet (500 feet VMC), working out the flaps at the prescribed speeds (since you so well planned the descent in the first place). And, you make a nice touchdown using the proper reverse and braking procedures to minimize brake wear.

You all get the idea...

Happy customers, minimal costs, keeping that widget machine going and going, because you baby it.

A result, job security, good pay, profitable business. Fast upgrades for the F/Os. (The bean counters purchase more widget machines.)

Or, the other side of the coin...If we had to, ourselves, pay for flap repair, brake replacement, fuel, etc., we'd operate a little differently.

The funny thing...we are paying for it, ourselves...just not directly and not obviously. But, we are paying for it.... Yep, we sure are!


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Old 1st Jun 2007, 09:57
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7 to 8000 above profile? How far from the airfield? The best you will safely achieve ( stable rod and thrust at 1000' agl) in any boeing is double the profile at 10 nm flown with flaps 25 gear down on 737 170 and gear down flaps 20 on 747 classic and 744 160knots. You will get a rod of 1500 or so and visually will see the aimpoint well short of the threshold until you are in the 3 degree slot. So that means 3000 above profile at 10 nm and configured. An extra 10 track miles doesnt mean an extra 3000 feet unless you are similarly configured. Racing towards the ground at high speeds is a problem unless you have greater than a 6G rating on your aircraft. If ATC is the problem then time to make a phone call and have a cup of tea to mutually understand each other then work out somewhere to orbit or race track and descend. The fuel considerations are minimal as you burn 40 kg a minute in a low level pattern of 4 minutes equals 160 kg. You only burn 300 kg in a complete descent so an idle descending holding pattern or orbit costs zip. regards
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Old 2nd Jun 2007, 12:26
  #32 (permalink)  
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... are you saying in absolutly no circumstance is it ever okay to violate a limitation or regulation? What is it exactly about my post you disagree with? ...

Peace, brother .. keep in mind

(a) this Forum has an educational thrust for the newer PPRuNe folk so those whose beards are greyer tend to emphasise the conservative

(b) regardless of your personal thoughts, the captain WILL be called on to account for his/her actions in the event of an incident or accident (presuming he/she survives the latter).

A colleague comes to mind whose experience following a fatal (in which he had no part) involved spending a day or two in the box with the wolves doing their best to attach blame to him and the company .. be VERY wary of thinking that the captain is some sort of holy (wo)man who can do his (her) own thing in isolation ...

(c) sure, the captain may do what is considered necessary in an emergency but consider (b) and the fact that the typical pilot has little knowledge of design, testing, and certification .. ie how "hard" is that limit which you are about to propose busting ... ?
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Old 3rd Jun 2007, 08:16
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John, thank you for your points... I understand your argument and tend to agree with what you said. Cheers!
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Old 5th Jun 2007, 21:25
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Back to the original question. I follow all the macho arguments, and all the techno discussions. However, the original scenario was the crew are offerd a visual approach. That would suggest they can fly in whatever part of the sky they wish to achieve the meeting of a/c with gound at the correct place and speed.
It is said the company limitations are not allowing orbits on finals, within certain criteria. I know some of the N.Italian airfields concerned where there is often an unhelpful tailwind on a straight-in. However, what prevents a flight through the centreline and capture form the other side? This is not an orbit. Or, a turn away from the finals until at suitable height?
The drive & dive technique works, yes, but it has the pax hanging in their straps and the cabin crew hanging onto the trolleys as they career towards the sharp end.
The clearance was a visual approach, not an expedite landing. There's no fire or any other justification to exceed, limits or operate outside SOP's.
However, if ROD is what is required then gear (any significant drag) is best, but if you are pointing at a runway with gear out/speed brake and 245kts then, perhaps, you are in the wrong place. It is not a comfortable feeling, wondering if it is going to work out, or not. Hairs on back of neck etc.
If you are offered a visual in a small airfield, it might imply no other traffic. Why not consider a flight over the airfield into a visual circuit? Safe, smooth and comfortable.
The skillful pilot avoids getting into situations where he needs to use his skills to escape from them.
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