KarlB737
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Ntsb Urges Pilots To Change Landing Calculations

Fri Dec 08, 2006 11:09 pm

Courtesy: Associated Press, South Bend Tribune

NTSB Urges Pilots To Change Landing Distance Calculations

http://www.southbendtribune.com/apps...icle?AID=/20061207/News01/61207012
 
CosmicCruiser
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 1:07 am

But Southwest spokeswoman Beth Harbin said Wednesday that the carrier continues to calculate thrust reversers into landings because it believes it gives a more accurate prediction of the landing performance.

"We believe having thrust reverser credit accounts for what will happen when you land," she said. "We believe you should factor that in, because that is the actual operation of the aircraft."

yep, and believing that when the margin is that close will get you exactly what they got. There are so many variables involved with using reverse that you cannot assume that every pilot will deploy the reversers the exact precise way every single time. How quickly does the pilot initiate reverse? Most jets require the nose wheel to be on the ground before going past idle. How quickly does every pilot lower the nose on landing? Do the reverse levers hang up because they may be pulled a little soon? Does every pilot use max reverse every time? And finally, what is the recommended procedure if you begin to yaw on a slippery runway? A. you get out of reverse straighten the jet and re-initiate reverse. So much for your stopping dist calculation using reverse. That's why most operators DON'T use reverse in calculating stopping dist.
 
planespotting
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 1:45 am

While I agree that reverser calculations should be factored in, there probably should be a higher margin of error to account for the different variables inherent in deploying the device (flare height, actual landing speed, reaction time, etc...).

Perhaps they should calculate the numbers as they do now, and simply add 5% of the length requirement to whatever number they came up with.

For instance, if a landing calculation with thrust reverse calls for a req. length of 4500 feet for a safe stopping distance, adding a 5% margin onto that would increase the length to 4725 (4500 feet * .05 = 225 feet). That extra margin would account for all the little unknowns that happen in a landing.

Keep in mind also that there are only a few runways in the US (the likes of BUR, MDW, etc...) where the available distance is short enough to cause a worry anyway.
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Yellowstone
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 2:26 am

I was under the impression that pilots were not allowed to factor in thrust reversers when calculating landing distances. Was this a recent change, or did I just have my facts wrong?
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Goldenshield
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 2:41 am

Quoting Yellowstone (Reply 4):
I was under the impression that pilots were not allowed to factor in thrust reversers when calculating landing distances.

Reversers are not allowed for certification; however, it is up to the operator and performance provider (if any is used) to determine whether reversers are to part of a performance calculation.
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AA737-823
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 2:44 am

Quoting CosmicCruiser (Reply 1):
Most jets require the nose wheel to be on the ground before going past idle.

Neeeeeegative.
Most aircraft don't have a nosewheel squat switch at all, much less require them to be squatted. If the nosewheel had to be on the ground to go past idle, then how, get this, would the aircraft FLY???

Most of the time, especially here at Anchorage, reversers are full-deployed long before the nose gear touches concrete. And they're spooled up, too.
Smaller aircraft may not be in as big a hurry, typically, since they need less runway than our 747s, but at Midway, I'd think they'd get the reversers deployed on final approach, about the time they lower the gear.
 Smile

P.S... the smiley face means that last part was a joke, since most people here don't seem to understand that.
 
redflyer
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 2:51 am

Quoting AA737-823 (Reply 6):
If the nosewheel had to be on the ground to go past idle, then how, get this, would the aircraft FLY???

I think the DC-10 and MD-11 have squat switches on the nose gear, but it's only for the #2 engine. I read somewhere that the #1 and #3 engines could go in reverse once the mains were down but the nose wheel had to be on the runway before the #2 could go in reverse. Something related to the nose gear never being able to come down all the way if the #2 went into reverse before then.
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CosmicCruiser
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 4:28 am

Quoting AA737-823 (Reply 5):
Neeeeeegative.
Most aircraft don't have a nosewheel squat switch at all, much less require them to be squatted. If the nosewheel had to be on the ground to go past idle, then how, get this, would the aircraft FLY???

I ASSUMMED you knew I was speaking of IDLE REVERSE. As REDFLYER points out the MD-11(which I fly), MD-10 and the DC-10 do use a nose squat switch that inhibits anything above IDLE reverse on No2. The 727 did not use a nose squat switch and if you used more than, again, IDLE reverse you could quite easily pitch the nose up with a resulting tail strike, especially on the -200. Therefore our ops man was explicit that you would not use more than ,again, IDLE reverse with the nose wheel off the ground.

Quoting AA737-823 (Reply 5):
, reversers are full-deployed long before the nose gear touches concrete. And they're spooled up, too.

Deployed is one thing(p.s. that's idle, in fact the MD-11 won't let you go past IDLE until they are fully deployed or otherwise you'd have forward thrust) but fully spooled up is another thing. On the 727 we used to hold the nose off and be cute but in the bigger jets that I've flown you get the nose down in a timely manner so deploying the reversers and spooling them up before the nose gets down just won't happen. I can't say about any 747,757 or 777 drivers and their ops.
 
planespotting
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RE: Ntsb Urges Pilots To Change Landing Calculatio

Sat Dec 09, 2006 5:10 am

Quoting AA737-823 (Reply 5):
Smaller aircraft may not be in as big a hurry, typically, since they need less runway than our 747s, but at Midway, I'd think they'd get the reversers deployed on final approach, about the time they lower the gear.

In the 737 initial ground school I attended as an intern, the pilots were told to never engage the reversers until the aircraft was on the ground...those engines aren't perfect machines, and I don't think you wanna have your airplane in a nose-up situation with only two mains on the ground when you engage your reversers...odds are, one will engage slightly before the other, and in that situation, do you really wanna have one engine full reversed whilst the other is operating in the regular mode, even if it is for a few milliseconds?

I'm pretty sure all airliners don't engage/deploy T/R until the a/c is fully on the ground (on all three gears.)
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2H4
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 7:12 am




Quoting Planespotting (Reply 8):
I'm pretty sure all airliners don't engage/deploy T/R until the a/c is fully on the ground (on all three gears.)

ahem...


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CosmicCruiser
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 7:37 am

You have to admit that's pretty rare. Most jets will fall out of the sky if you did this.
 
2H4
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 8:02 am




Quoting CosmicCruiser (Reply 10):
You have to admit that's pretty rare. Most jets will fall out of the sky if you did this.

Oh, absolutely. I just thought it was a fun illustration of how widely procedures can vary from one aircraft to another.  Smile


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OPNLguy
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 8:07 am

Quoting 2H4 (Reply 11):

Oh, absolutely. I just thought it was a fun illustration of how widely procedures can vary from one aircraft to another.

If memory serves, the old DC-8s (non-CFM) could also use reversers in-flight, but only on the #2 and #3 engines....
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jhooper
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 2:24 pm

....in my specific MILITARY aircraft, our landing data is based on using Reverse IDLE, and a number of other operational factors that are rarely realized in the real world, such as max anti-skid braking applied within 1.5 seconds of touchdown.
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OldAeroGuy
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 3:15 pm

Quoting 2H4 (Reply 9):
Quoting Planespotting (Reply 8):
I'm pretty sure all airliners don't engage/deploy T/R until the a/c is fully on the ground (on all three gears.)

ahem...

This is the sort of thing you do when your engines have lousy spool up time.

It does make go-around easy since once you retract the reversers, the engines are providing plenty of thrust.

However, it sure does produce alot of approach noise. No QC2 operation for this configuration.
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CosmicCruiser
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 11:23 pm

Quoting OldAeroGuy (Reply 14):
It does make go-around easy since once you retract the reversers, the engines are providing plenty of thrust.

I'm not really sure I follow you here. I've never flown a jet that didn't go back to idle when you stow the reversers therefore you're still starting from idle thrust. For our ops once reverse is initiated you're obligated to staying on the ground. That's the reason say on the MD-11 that the reverse is locked at IDLE until the are fully deployed; conversely when you come out of reverse you don't want a burst of forward thrust as you stow them so you're back at idle.
 
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scbriml
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 11:38 pm

Quoting CosmicCruiser (Reply 10):
You have to admit that's pretty rare. Most jets will fall out of the sky if you did this.

Maybe not for the Russians! wink 

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longhauler
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RE: Ntsb Urges Pilots To Change Landing Calculations

Sat Dec 09, 2006 11:49 pm

Some of the earlier B737-200s I flew had a nosewheel squat switch inhibiting reverse until tripped. This was so that you couldn't scrape the buckets on the ground when in transit.

I used to think it was a bunch of hooey, until I watched one of our aircraft landing without a squat switch and was amazed how very close the buckets do come to the ground when in transit to reverse in a nose high position on touchdown.
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