Thrust to flare?

[ImbracableCrunk]

I've seen this technique a few times now with different pilots:

A few feet off the deck in the flare, the pilot jams the T/L forward and pulls it back just as rapidly. It wasn't for a gust, just for. . . ?

I can think of a few reasons not to do this. Can anyone come up with a good reason to do this? 737CL-NG.

[Yobbo]

What type of a/c ? T-tail with tail engines or under wing engines?

[ImbracableCrunk]

B737 Classic and NG.

[captjns]

Technique for the 727.

[ImbracableCrunk]

Thanks for the ideas.

Hmm. One or two might have been former 727 drivers. Seems like some of the shorter fields, that won't help matters at all.

Why on the 727? Vertical component of thrust to soften the touchdown? Why not just flare with the yoke?

[pattern_is_full]

Why on the 727?

Probably fodder for a separate thread, but the 727 had a reputation for hard touchdowns if power wasn't kept up through the flare. A whole separate "Tech-Log" debate in itself, but one of the reputed reasons was that the massive triple-slotted flaps could kill airspeed so fast that an unpowered flare simply turned into a 5-foot free-fall.

http://www2.tech.purdue.edu/at/courses/aeml/airframeimages/727flap.jpg

I guess it depends on which market one is flying in, but it would surprise me if there were many 727 pilots still transitioning to 737s (and bringing along old habits) at this late date.

[grounded27]

Brings back the stories I had been told that a single notch flaps would improve cruise performance in a 727? Only damb aircraft I had ever shimmed the I/B and O/B flaps for low speed and high speed aileron trim issues.

[blind pew]

Watched a few guys do it on the DC9 - but a quick dab of stab trim worked just as well without the theatricals...
As stated tendency to counteract running out of energy in the flare - had similar on the early Twin astir - grob 109 glider - and had to half retract the airbrakes for the flair.

[Cough]

Used the technique when a high sink rate has developed just prior to touchdown, works wonders! However, routine use????

[stilton]

As you said, if you need it to counter a high sink rate close to the ground fine, otherwise it's a bad habit and can lead to other problems one of which is running out of runway !


Barring a last minute high rate of sink requiring power you will always get a better landing touching down with idle thrust.


And that includes the B727 :ok:

[captjns]

I loved every hour of my 5,000 hours as a skipper of best airplane Boeing built (MHO of course). I sure miss my F/E too. But life goes on.

The 727-100 series does not need the punch of thrust beforetouchdown as the stretched 727-200 needs. The -100 series is an extremely well balance jet aerodynamically speaking. Like a light twin one can chop the power,flare and make a normal landing within the 1,000’ runway markings with consistency.

The 727-200 has much different characteristics during theespecially during the last 50' of the landing phase. If one flares the jet withback pressure, the mains will be driven onto the runway as the center of liftis forward of the mains. It’s takes acoordinated effort to make a proper landing… a punch of thrust to help check the decent, and actually abit of forward pressure to ensure a nice touch down. No float and always within 500’ of the 1,000’marker. A nice feature about the 727 is when the power comes off thejet does not float like the 737.
I used the same technique with airports with 5,300’ runways inthe Caribbean and Tegucigalpa before they blew off the top of the mountain southRunway 02 which now has about 5,500’ of useable runway beyond the threshold.

Barring a last minute high rate of sink requiring power you will always get a better landing touching down with idle thrust.

And that includes the B727 http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/thumbs.gif

That said, Stilton, many -200 drivers and MD80/90 pilots may not agree with your assertion.

[JammedStab]

I loved every hour of my 5,000 hours as a skipper of best airplane Boeing built (MHO of course). I sure miss my F/E too. But life goes on.

The 727-100 series does not need the punch of thrust beforetouchdown as the stretched 727-200 needs. The -100 series is an extremely well balance jet aerodynamically speaking. Like a light twin one can chop the power,flare and make a normal landing within the 1,000’ runway markings with consistency.

The 727-200 has much different characteristics during theespecially during the last 50' of the landing phase. If one flares the jet withback pressure, the mains will be driven onto the runway as the center of liftis forward of the mains. It’s takes acoordinated effort to make a proper landing… a punch of thrust to help check the decent, and actually abit of forward pressure to ensure a nice touch down. No float and always within 500’ of the 1,000’marker. A nice feature about the 727 is when the power comes off thejet does not float like the 737.
I used the same technique with airports with 5,300’ runways inthe Caribbean and Tegucigalpa before they blew off the top of the mountain southRunway 02 which now has about 5,500’ of useable runway beyond the threshold.



That said, Stilton, many -200 drivers and MD80/90 pilots may not agree with your assertion.

The 727-200 does not need a burst of thrust in the flare. I have heard of this technique and it may work, but it can be landed just fine by doing a normal approach and landing(admittedly mine were all flaps 30). Bring the thrust off in the flare. Seem to remember that it was at about the 20 foot autocall. Most landings were decent, some were firm and some were greasers. Some guys flared and then pushed a bit, some on occasion just gave a forward push on a short runway(good for spot landing but you knew when you touched down). Sometimes just a normal bit of a pull worked as well.

It certainly was not a requirement to add a burst of power to get a normal landing with flaps 30.

[captjns]

It certainly was not a requirement to add a burst of power to get a normal landing.


I should have made a clarifying statement that the burst ofthrust was a technique I adopted. As theold saying goes “whatever works…”

[Tee Emm]

The "burst of power" addiction (and believe me it is an addiction) is common to many pilots flying the 737. These pilots have picked it up from watching other pilots or listening to war stories from olde captains who may have flown the 727. From these myths they then think it is a real cool method of getting a smooth touch down.

Interestingly, you don't see much of this technique in the simulator yet it is relatively common among certain pilots in the real aeroplane. Inevitably the aircraft floats and lands long, albeit often smoothly. That makes the pilot real happy and he is now convinced for the rest of his career that a burst of power is the key to smooth landings.

Other new pilots watch him and the technique is perpetuated. Of course there are times when additional power is called for near the flare but it is not a standard technique for normal landings and needs to be severely discouraged as bad flying technique

[ImbracableCrunk]

I'm guessing that JT-9D have a much quicker spool-up and -down time than a CFM-56.

A "short jab" on the JT-9D might be more of a "slow swipe" on the CFM-56.

Either way, the last guy I flew with grumbled, "Damn -900s" as we limped off the runway. No softening about it.

[stilton]

Captjns


Seven years on the B727 and four on the MD80.


Idle thrust at touchdown was the flight manual procedure and, to reiterate, unless power was required to correct a high sink rate always resulted in a better landing.


Some may disagree but these were the guys I saw porpoising down the runway with their experimental homemade techniques.


They never got a predictable result but they used up a lot of runway believing in a myth these Aircraft could not be landed like any other jet transport.

[sevenstrokeroll]

there are some reasons, good or not is up to you.

1. when you jam on thrust what happens on a 737? the nose goes up...underwing engines will push nose up ...cutting power brings nose down

2. Airplanes get bent up in real life...wing leading edges get roughed up in real life...if you cut power too soon the drage may make the plane slow down a bit faster than the ''ideal'' brand new plane or simluator.

3. Here is a real help...if you and the engines are spooled up just at touchdown, they will be more available for reverse thrust...in other words jam up the throttles, engines spool up and retard them allowing reverse thrust selection and the reverse thrust is available more quickly as the engines are still spooled up

4. It is possible the pilot is adding the thrust because he has perceived a high sink rate developing and you haven't

6. notice I missed five?

5. I've flown botht the DC9 and 737. DC9 is my favorite. and a quick burst of power is used when a high sink rate develops near the end, usually if the airfield is blanked by trees, cutting off the wind or if there is windshear for other reasons. judging sink rate can be a very ''seat of the pants'' thing.

so ask yourself if the pilot is doing it at fields where the trees blank the wind

[KAG]

For the "long" 737 like the 800, 900 (and even the 300 maybe) the flare is sensitive and that's not easy to decrease the sink rate below 200/150 ft per minute (that should give you a standard load) with flaps at 40, but quite easy if you keep some thrust til touch down. Thing is keeping thrust during touch down is not standard procedure for many reasons, one being, for example, that the speed brake won't deploy automatically, so one method is the one you mention, it gives you thrust during touch down (the engine don't have time to come back to idle) while the thrust handle is at idle and the speed brake will deploy with a lower pitch up attitude that should prevent any bounce.
However the ones able to master this non standard technique are the ones already confortable with the standard, normal flare. Useless then at the end.

[de facto]

judging sink rate can be a very ''seat of the pants'' thing.

Looking outside too...

[captjns]

As I posted before Stilton... it was my technique. Just a burst of thrust to arrest the decent and off for the touchdown. No float, and no porpoise down the runway. By the grace of the Sky Gods, I never ran off the 5,500' runways I operated into. At least the good old 727 has normal approach speeds and powerful brakes versus newer generation jets of today. I will say this however, getting out with -9s could be a challenge at times... but that is a topic for another thread.

I've never seen jets test flown to or from short runways, and as Joe Petroni said, "Good thing the B707 can't read.". Well either could the 727.

[ImbracableCrunk]

Well, I flew another sector with said pilot, and I asked him about his background: 727 (FE), DC-9, MD-80, and 737.

I'll estimate I've flown with well over 300 pilots on the 737, but for simple math: 300 pilots and 3 of which use this technique. 1% use this technique. I've flown with many former 727 and DC-9 pilots who do not use this technique.

The last leg we flew, he jockeyed the power around 40-60+ % in the flare-float and took the jet to the end of the runway. There was no shear/gust/high sink.

Not impressed with this technique, but thanks to all for the interesting input.

[sevenstrokeroll]

crunk...one thing I have learned about pilots is this:

at some point, you get the sweetest landing you ever had and you used an unusual technique. so, somehow you think...gee if` i can only do that again

and they use a nutty technique...just hoping.

well, they got lucky once, but they learned to be stupid.

I knew a dc9 captain who trimmed into the flare on every landing...his landings wer pretty good...but I told him that if I was the captain I would tell him not to do it that way as the technique will bite you in the butt one day.

you might even use the same phrasing to tell the pilot he is wrong.

once in awhile a burst of thrust does save things...but to do it all the time may mean he has vision problems!

[aerobat77]

the pilot jams the T/L forward and pulls it back just as rapidly. It wasn't for a gust, just for. . . ?

just for coolness , and jamming a turbofan for a burst is as smart as some comments here gents.

[FlightPathOBN]

For the "long" 737 like the 800, 900 (and even the 300 maybe) the flare is sensitive and that's not easy to decrease the sink rate below 200/150 ft per minute (that should give you a standard load) with flaps at 40, but quite easy if you keep some thrust til touch down.

exactly, and with the coded FP, the 2.8 GPA is becoming the standard...

[18-Wheeler]

When I was on the 747 Classic freighters if we were up around the 285 tonne max landing weight I'd start the flare when the 30' auto call was made and leave the approach power on until the nose had pitched that 2° pitch more up, then pull the power off and it'd settle nicely.
Down around the 180 tonne mark, cut the power at the 20' call and pitch, etc.

[stilton]

What the power on crowd don't see is that you are basically 'powering into the ground'


This will nearly always produce a harder landing than the manufacturer's recommended idle thrust touchdown.


I doubt there is a flight manual out there that recommends (outside of correcting a last minute high sink rate) landing with other than idle thrust on a jet transport.

[Loose rivets]

Whether we know it or not, we react to seat of the pants sink. At least, I hope we do. Trees mentioned some posts ago. Hangers, or a mischievous wind, you can't plan for it. A sudden sink towards the concrete would get a power reaction from me, even before it had registered in my higher thinking processes. :rolleyes:

As is evidenced by:

Interestingly, you don't see much of this technique in the simulator

My pants never gave me clues in a sim.

[jimsmitty01]

This is definitely not a normal technique, but can be used when landing on a longish runway and having a high sink rate during the flare due to a loss of energy over threshold (caused by all sorts of different factors, but commonly a loss of headwind). I find a small well timed increase in thrust can reduce the rate of descent on the B737 NG. The under slung CFM 56's produce quite a large thrust / pitch coupling, so this small increase in thrust does two things to reduce the ROD. 1) Replaces lost energy 2) Small increase in pitch attitude.

There is scope for things to go wrong. Too much added thrust, badly timed and for no reason, can lead to a balloon and float effect... not ideal at all!

[root]

A well-timed burst of thrust may make the difference between a firm touchdown and an over-G touchdown in difficult situations.

During regular landings there's usually no need for it.

[ManaAdaSystem]

There is another silly way to make good landings, always add 20 kts and float down the runway to a smooth landing.
Unless the weather dictates otherwise, idle landings will give you the shortest landing distance. That is all I care about. A smooth landing is not a good landing unless it is done at the correct spot at VRef -5 and at idle thrust.
In my career, I have only come across one pilot pushing the throttles up just before touch down. He would ALWAYS land at Vref + something and would ALWAYS use more runway than required.

[412SP]

If you get a little slow, add the power.

If it's a regular technique, it's purely sloppy.

:=

[misd-agin]

Sloppy, lousy technique. Not uncommon on the 727. New FO's would be told the ususal B.S. "don't land at idle because the plane will fall out of the sky." :ugh: Almost every 727 landing was at idle.

727 flaps 30 is less tricky than a 737NG with flaps 40. I'd estimate a 727 flaps 30 would be like landing a 737NG with flaps 35.

[Loose rivets]

Isn't this all getting away from the point? In particular:


If you get a little slow, add the power. If it's a regular technique, it's purely sloppy.


I would have thought the only justification for taking the engines through a sizable temperature cycle, and possibly making your field performance a little iffy, would be if the aircraft suddenly increases its sink rate and you had to do something.

There are aircraft where landing performance is based on throttles closed in the air. In a short field situation on jet transport aircraft, I personally liked to be a tad deeper into the drag curve and with stable commensurate power. It really did give the spool-up improvement needed to cope with nature's surprises. But, a late-state engine failure had to be built into one's cunning plan.

[sevenstrokeroll]

the best advice for a smooth landing in a jet transport.

stable

flare

and then reduce the power

not reduce power and then flare.

j

ps... as I said and no one mentioned...spooling up just before flare means you will be ahead of the game in thrust reverse.

[aterpster]

A 727 skillfully flown into the flare at V2+10 can usually have power reduced to idle prior to touchdown.

Unstable winds are a different matter, just as they are for most airline birds.

[aterpster]

ps... as I said and no one mentioned...spooling up just before flare means you will be ahead of the game in thrust reverse.

Somehow, I got through my 27 years without ever having done that, knowing that, or having been trained to do that.

[ImbracableCrunk]

If a modern jet engine with cascade-type engines only diverts part of the thrust for reverse, how can it be that adding thrust can be a good thing in the flare?

I'm all ears if someone's got some actual physics to back it up, but the same energy that is "improving" reverse thrust once you're on the ground has just pushed you 500' further down the runway.

Engines are more efficient at creating forward thrust than reverse.

[aterpster]

FlightPathOBN:

exactly, and with the coded FP, the 2.8 GPA is becoming the standard...

Do you have a reference for that?

Also, do you have an example of it in the U.S.?

[JammedStab]

ps... as I said and no one mentioned...spooling up just before flare means you will be ahead of the game in thrust reverse.

Isn't that why some of these modern engines like the GE CF-6 have something called approach idle. Your engine is already spooled up for you. Seem to remember something called High Idle on some PT-6 equipped aircraft such as the King Air.

[thermostat]

IMHO it depends on the type of engine on the 'craft. Back in the old days on the 727, power was never put to idle until close to the landing. These were not "fan" engines. In today's big fan engines, where the fan produces 75% of the thrust, I would start to reduce power at 50 feet and be at idle by30 feet, raise the nose to 6 degrees on the horizon and kiss the ground softly. Couldn't do that on the 727.
T

[FoxHunter]

There are three ways to reduce the sink rate landing the MD11 or MD10 1) Power, 2) Power, 3) More Power. Save a hard landing with pitch will only give you a very hard landing.

[fdr]

there was one airline that used to call "100ft" on the radar altimeter, at which point the pilot (almost always an ex F-5A major) would start running the trim fully back on the pickle switches. Yes, eventually the aircraft would land, in spite of the technique, usually also even on the runway, although there were many skidmarks passing across the piano keys, referred to as "Kong trails". Go arounds were not frequent but apparently very exciting.

If you need to add power on the aircraft in the flare from a stable approach, and you are not a helicopter... then it is hard to see that it complies with the certification standard, and I would doubt that it is in the FCTM for the type. For a decaying airspeed or increasing sink rate, keeping power on or adding power is a fair alternative to a hard impact, but by definition would not be considered as a stable approach.

B727: pitch down/deflare, power up etc, yes they get done, but oddly enough, the plane also lands very nicely with a gentle flare as per the FCTM, and reducing thrust to ide by touchdown, odd but true. MD11, seen many variations, like the B767, but the outcome from a normal approach and flare is about as nice and far less exciting. The MD does like to sink though...

[aozc]

I'm very new in this profession with only 260h on type. On steep GP-angles with headwind reducing abruptly it works great around the threshold not to lose the bugspeed, otherwise I don't see the point.

I've flown with a couple of captains (all ex military) who uses this technique even in perfectly normal conditions. Some also tend to jerk the yoke stick back very intermittently during the flare. They land the aircraft smoothly in general but in the far end of the TDZ.

I just move my eye-focus to the far end of the runway and try to coordinate 0 sink with one meter below the runway using my peripheral sight. That way I don't end up with these PA28-floats (the 737 floats like a fat lady in a tub of salt water) that many of my mates do :} less brake wear, reversing and backtracking. Also a faster vacation of the runway.

It keeps my acc. manager, Boeing, captains and maintenance happy. The only one taking a turn is my ego, haven't managed to get one yet though :E

[VinRouge]

This is how the C-17 "Flares". However, there is a shedload of flight control law mechanics also working in the background, in particular alpha hold functions and using the trim switch to control IAS (so I am told).


If you had a HUD with a flight path vector displayed, you would see the mechanics of it.

I used this technique on the herc J, it provides extra lift and an upward motion of your flight path vector especially as you approach ground effect (which is also visible through a hud). We used it as an untought technique on some of the longer strips in afghanistan to prevent the aircraft slamming in on what would otherwise be a needlessly agressive touchdown (the manual is written for short field performance). The effect is instantaneous and does not result in a speed increase, its done literally as you enter ground effect and thus the extra thrust does not have time to accelerate the aircraft.

Whether it would work on an aircraft without barn door type flaps I dont know (not sure if it is blown lift or due to the thrust affecting circulation).

Biggest problem with it is the gentle touchdowns it generates can delay spoiler deployment and potentially invalidate your TOLD calcs. Its also almost impossible to judge touchdown point and if you overdo it, you can end up climbing!