Turbulent Approach Less Flaps
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I tried several times to log in using the same password but was unable to. Finally I got in. Is there something wrong with the site????????
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Thermostat
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Thermostat
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Flaps on approach
I seem to remember that the drag goes up with the square of the lift. If you double lift, the drag goes up four times. Triple lift and the drag goes up NINE times. So the more flap you use, the more lift you produce but the drag goes up quite a bit (with the square of lift). During turbulent approaches, if flap is reduced, drag is also reduced, speed is increased and that helps to improve approach and go-around performance if required.
I well remember the L1011 that crashed going into Dallas years ago. Got into a microburst and couldn't maintain the flight profile. It's possible that a reduction of flap may have saved the day.
T
I well remember the L1011 that crashed going into Dallas years ago. Got into a microburst and couldn't maintain the flight profile. It's possible that a reduction of flap may have saved the day.
T
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Meikleour,
I agree 100% regarding the fuel situation and things did change as a result of the incident. To be fair to the crew, at the time, the manuals were not very clear on a couple of the finer points of the fuel system but that has been rectified and I'm confident the situation in which they found themselves would not happen nowadays.
For what it's worth, the incident shouldn't even be in this thread. I only wrote about it because of SSR's bigoted accusation of what they did was wrong, because it doesn't conform to what he would have done. The actual flight has been done to death on PPrune and it's clearly got nothing to do with flap settings, so hopefully that'll be an end to it
I agree 100% regarding the fuel situation and things did change as a result of the incident. To be fair to the crew, at the time, the manuals were not very clear on a couple of the finer points of the fuel system but that has been rectified and I'm confident the situation in which they found themselves would not happen nowadays.
For what it's worth, the incident shouldn't even be in this thread. I only wrote about it because of SSR's bigoted accusation of what they did was wrong, because it doesn't conform to what he would have done. The actual flight has been done to death on PPrune and it's clearly got nothing to do with flap settings, so hopefully that'll be an end to it
Pontius: Thanks for your reply.
THE LAW OF UNINTENDED CONSEQUENCES
My personal interest in that incident stems from my own experience many, many moons ago when I worked for one of the companies that became BA. Your loyalty to BA is understandable however that company has always had a tendency to change/rewrite perfectly good manufacturer's manuals into their own version. I was very nearly caught out by just such a situation involving an emergency gear extension which did not work as per the BA drill and indeed the poor -400 crew were let down in a similar manner.
I do however draw the line at your assertion that the flight was perfectly safe when in the end the crew felt that they had to declare an emergency!!
Going back to the original thread - the various manufactures go to great lengths to produce operating procedures that work and do not require "exceptional pilot skill" therefore there should be no need to debate the merits or otherwise of different flap settings. I am fully aware that some individuals will always know better however.............
THE LAW OF UNINTENDED CONSEQUENCES
My personal interest in that incident stems from my own experience many, many moons ago when I worked for one of the companies that became BA. Your loyalty to BA is understandable however that company has always had a tendency to change/rewrite perfectly good manufacturer's manuals into their own version. I was very nearly caught out by just such a situation involving an emergency gear extension which did not work as per the BA drill and indeed the poor -400 crew were let down in a similar manner.
I do however draw the line at your assertion that the flight was perfectly safe when in the end the crew felt that they had to declare an emergency!!
Going back to the original thread - the various manufactures go to great lengths to produce operating procedures that work and do not require "exceptional pilot skill" therefore there should be no need to debate the merits or otherwise of different flap settings. I am fully aware that some individuals will always know better however.............
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The poor guy that initiated this thread is probably more confused now than the beginning. I would say if the operating manual says you need to or can use discression on flap settings and your op specs agree do what works best for you. I personally usually used the max setting unless performance required otherwise but others feel differently. Never once had a problem using that procedure. As long as it is legal who can fault you?
I think there is lot of argument (some healthy) over this subject as there isn't really a 'right' answer that covers every aircraft type, runway and weather condition.
In no particular order, here are some of the things that might be considered on a bumpy day when choosing a land flap setting in a jet transport:
Advantages of lower flap setting:
* Higher Vref gives greater control authority
* Less drift angle
* Less drag, so better performance in windshear
* Often greater margin to flap limit speed
* More fuel efficient
Disadvantages:
* Longer landing roll
* More variation in speed due less drag
* Engines less responsive as lower thrust setting
* Easier to carry excess speed into the flare
* More energy into the brakes
* Tailstrike more likely in some types
Advantages of higher flap setting:
* Shorter landing roll
* More stable airspeed
* Engines more responsive
* Lower pitch attitude
* More time to adjust flightpath
* Minimises brake temperatures
Disadvantages:
* May need more control application
* Often close to limit/relief speeds in turbulence
* Loss of airspeed in the flare may need prompt action
* Less fuel efficient
If I was landing on a long-ish runway with a headwind component, I'd probably go for the lower flap setting. A wet and/or shorter runway, tail wind, high landing weight and/or high density altitude would have me fully configured. The books usually say I could land with either but I have a strange aversion to planning the use of a large percentage of the available runway if there is an option to use less...
In no particular order, here are some of the things that might be considered on a bumpy day when choosing a land flap setting in a jet transport:
Advantages of lower flap setting:
* Higher Vref gives greater control authority
* Less drift angle
* Less drag, so better performance in windshear
* Often greater margin to flap limit speed
* More fuel efficient
Disadvantages:
* Longer landing roll
* More variation in speed due less drag
* Engines less responsive as lower thrust setting
* Easier to carry excess speed into the flare
* More energy into the brakes
* Tailstrike more likely in some types
Advantages of higher flap setting:
* Shorter landing roll
* More stable airspeed
* Engines more responsive
* Lower pitch attitude
* More time to adjust flightpath
* Minimises brake temperatures
Disadvantages:
* May need more control application
* Often close to limit/relief speeds in turbulence
* Loss of airspeed in the flare may need prompt action
* Less fuel efficient
If I was landing on a long-ish runway with a headwind component, I'd probably go for the lower flap setting. A wet and/or shorter runway, tail wind, high landing weight and/or high density altitude would have me fully configured. The books usually say I could land with either but I have a strange aversion to planning the use of a large percentage of the available runway if there is an option to use less...
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FW, I agree with your analysis. We all have found what works for us and are comfortable and successful using that technique. Why change it because some other pilot finds a different way of doing it works better for him?
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Nice post FullWings.
Thought I might add one.
On some aircraft, less flap can mean more difficulty slowing to approach speed while maintaining minimum approach thrust. On the 727-200 with a Raisbeck hushkit and a maximum of Flaps 28, at light weights it was difficult to slow down to approach speed at minimum EPR.
Thought I might add one.
On some aircraft, less flap can mean more difficulty slowing to approach speed while maintaining minimum approach thrust. On the 727-200 with a Raisbeck hushkit and a maximum of Flaps 28, at light weights it was difficult to slow down to approach speed at minimum EPR.
Its been an interesting journey through this thread with some amazing drift off topic, good to see that it's back on track. BARKINGMAD made the best observation some time back. In turbulence and limiting crosswinds its an advantage to reduce flap, where permitted, because the spanwise lift distribution moves outboard and increases roll response. The reduced drag also improves speed recovery in gusts. Try landing at flap 30 in a B777 in turbulence and a circa 40kt crosswind and you can reach full roll input at times. Flap 25 makes it much easier to manage.
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Spoiler response V Aileron response
I fly the A320 and always use Conf 3 rather than Conf Full in gusty/crosswind conditions, primarily for better controllability.
From what what I have read, Conf Full on Airbus uses a lot of spoiler deflection for roll control, and the response of spoiler deflection is not linear ( unlike aileron deflection ) leading to overcontrolling and PIO.
For myself, Conf 3 with more "normal" aileron response makes the 320 fly like my previous non-FBW types, and makes the gust corrections much easier.
I am not a test pilot, so if another explanation is correct, I would be happy to stand corrected.
From what what I have read, Conf Full on Airbus uses a lot of spoiler deflection for roll control, and the response of spoiler deflection is not linear ( unlike aileron deflection ) leading to overcontrolling and PIO.
For myself, Conf 3 with more "normal" aileron response makes the 320 fly like my previous non-FBW types, and makes the gust corrections much easier.
I am not a test pilot, so if another explanation is correct, I would be happy to stand corrected.
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Static lateral stability
I think that the main advantage of lower flap setting for approach in gusty/ crosswind is slower reaction aircraft on changing in sideslip.
In gusty wind sideslip is continuously fluctuating and aircraft is continuously banking from side to side due to static lateral stability.
(see http://aviacom.ucoz.ru/Book_13_Principles_of_Flight.pdf, Chapter10, page 302)
All contemporary aircrafts have swept wing and this lead to excessive static lateral stability (see pages 306, 307 and figure 10.62).
The more Cl (coefficient of lift) we have - the more "dihedral effect" we have, and we have to counter the more sharp lateral aircraft movements.
In gusty wind sideslip is continuously fluctuating and aircraft is continuously banking from side to side due to static lateral stability.
(see http://aviacom.ucoz.ru/Book_13_Principles_of_Flight.pdf, Chapter10, page 302)
All contemporary aircrafts have swept wing and this lead to excessive static lateral stability (see pages 306, 307 and figure 10.62).
The more Cl (coefficient of lift) we have - the more "dihedral effect" we have, and we have to counter the more sharp lateral aircraft movements.
