corey07850
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Reversers In Landing Calculations

Sat Jan 28, 2006 7:43 am

http://www.cnn.com/2006/TRAVEL/01/27/airplane.landings/index.html

Following the Southwest MDW accident, the NTSB is insisting that the FAA mandate thrust reversers be taken out of landing distance calculations on wet runways....

My question is: Doesn't the FAA already not allow reversers to be used in landing distance??

The article states that the FAA prohibits it in "some" cases... If so, what are these cases?
 
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Starlionblue
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 7:47 am

Quoting Corey07850 (Thread starter):
My question is: Doesn't the FAA already not allow reversers to be used in landing distance??

The article states that the FAA prohibits it in "some" cases... If so, what are these cases?

It's actually the other way around. The FAA allows reverser effect to be included in some cases. In most cases, such as dry runways, they are not allowed.

And now I'll let the experts tell you exactly when they are allowed.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
bohica
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 7:48 am

As far as I know thrust reversers are NOT to be considered in calculating landing distances under any circumstance. Please correct me if I'm wrong.
 
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Starlionblue
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 7:55 am

Quoting Bohica (Reply 2):
As far as I know thrust reversers are NOT to be considered in calculating landing distances under any circumstance. Please correct me if I'm wrong.

They may sometimes be used in certain wet runway circumstances.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
bohica
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 8:41 am

Quoting Starlionblue (Reply 3):
They may sometimes be used in certain wet runway circumstances.

If that's the case, I stand corrected. Thanks.
 
airfoilsguy
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 9:16 am

If a plane over runs the runway and crashes and a contributing cause is thrust reverser failure, does that absolve the manufacturer or airline of liability? Also, why have thrust reversers if the FAA, in essence, says they are not needed?
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FDXmech
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 12:08 pm

Quoting Airfoilsguy (Reply 5):
Also, why have thrust reversers if the FAA, in essence, says they are not needed?

I think many people think because thrust reversers (T/R's) aren't taken into the takeoff or landing stopping equation that they aren't effective.

An easy assumption to make but untrue.

The reason T/R's aren't figured in is to ensure stopping distances are determined as conservatively as possible using only basic stopping equipment, brakes. And even the brake effectiveness are based upon all brakes being worn to the maximum limit thus limiting their ability to absorb kinetic energy.

Stopping distances are determined sans the T/R's. But the aircraft can't be dispatched with more than one T/R inop.

T/R's have a relatively high failure rate, better to err on the side of safety and not rely on them when for a predictable stopping distance. And regulations say you can't.
You're only as good as your last departure.
 
2H4
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 12:18 pm




Quoting FDXMECH (Reply 6):
Stopping distances are determined sans the T/R's.

But certain aircraft can legally land using stopping distance data that is predicated upon the use of thrust reversers.




2H4


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IAHFLYR
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 12:43 pm

Landing data is based on BRAKES only!
Any views shared are strictly my own and do not a represent those of any former employer.
 
FDXmech
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 12:45 pm

Quoting IAHFLYR (Reply 8):
Landing data is based on BRAKES only!

Takeoff data also.
You're only as good as your last departure.
 
2H4
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 12:55 pm




Quoting IAHFLYR (Reply 8):
Landing data is based on BRAKES only!

Well, here's what Barney Captain (a current 737-700 captain) had to say about that in another thread:

I've been avoiding comment on this topic (for obvious reasons) but I would like to clarify one thing: the -700 was certified using reverse thrust for landing. We use an on board performance computer (opc) to calculate T.O. and landing data. From our F.O.M.; "The opc on the 700 takes into account the thrust reverser's for landing,certificated that way, unlike most other aircraft."

It's true the classic fleet (and every other a/c I'm aware of) considers reverse thrust for landing simply a bonus. Not the -700.





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IAHFLYR
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 1:01 pm

Quoting 2H4 (Reply 10):
It's true the classic fleet (and every other a/c I'm aware of) considers reverse thrust for landing simply a bonus. Not the -700.

Most intersting since a Boeing Test Pilot gave me that info and he also was part of the 700 cert! MMMMMM
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2H4
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 1:11 pm




Quoting IAHFLYR (Reply 11):
Most intersting since a Boeing Test Pilot gave me that info and he also was part of the 700 cert! MMMMMM

I'm guessing we're dealing with two different definitions of landing data. The Boeing test pilot might not have been quoting numbers specific to part 121 ops.

Or, he might not have gone into depth and specified the -700 exception, figuring the listener might not be interested in details and exceptions.

Regardless, I doubt a current -700 captain would have been operating under an illegal and incorrect set of regs for all this time.




2H4


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FDXmech
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 1:55 pm

I'm a bit confused about the 737-700 opc taking into account the thrust reversers.

Here's why.

On the performance computer at FDX, the default status for reverse thrust is they're both operating.

If a reverser is inop - the landing distance does not increase.

My question is this; On a SWA 737-700 opc - what is the default reverser status.

Are the reversers default operational with a commensurate increase in stopping distance on the opc if a reverser is inop?

Or is landing distance defaulted to a no reverse thrust condition but stopping distance adjusted downward by inputting both reversers operational?
You're only as good as your last departure.
 
2H4
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RE: Reversers In Landing Calculations

Sat Jan 28, 2006 2:03 pm



Great questions, FDX....and well over my head. If I can find out, I'll let you know.




2H4


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CosmicCruiser
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RE: Reversers In Landing Calculations

Sun Jan 29, 2006 12:05 am

Quoting FDXMECH (Reply 13):
On the performance computer at FDX, the default status for reverse thrust is they're both operating.

If a reverser is inop - the landing distance does not increase.

FDXMech has the right answer, at least for all ops that I'm aware of. I was always told that a couple of reasons that T/Rs are an added bonus is in older jets that required you to spool the engs. to a specific max. rpm, unlike some newer jets that protect you from over boost, you could never be sure from pilot to pilot that max was really set and also on slippery rnys if you lose directional control (say weathervane) then you're taught to come out of reverse, regain control and then reapply reverse. Again you can't count on having it all the way thru the stop.
There are numerous "pads" built in to performanc data to ensure defaulting to the conservative side and as FDXMech said this is one of them. Consider a rejected t/o due to an eng. failure, now you're stopping without all your reversers.
If indeed the 737-700 DOES use T/R in their perf. data it's the first one that I know of but hey I never flew one either. Considering the rumor still exists here at FEDEX I may see one yet! Hey,the A380 just made it to the standing bid choices.
 
FredT
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RE: Reversers In Landing Calculations

Sun Jan 29, 2006 1:24 am

First off, part 121 etc are operational procedures. You need to look at FAR25 for the certifying requirements.

Far 25.109 states that:

"(e) Except as provided in paragraph (f)(1) of this section, means other than wheel brakes may be used to determine the accelerate-stop distance if that means--]
(1) Is safe and reliable;
(2) Is used so that consistent results can be expected under normal operating conditions; and
(3) Is such that exceptional skill is not required to control the airplane.
[(f) The effects of available reverse thrust--
(1) Shall not be included as an additional means of deceleration when determining the accelerate-stop distance on a dry runway; and
(2) May be included as an additional means of deceleration using recommended reverse thrust procedures when determining the accelerate-stop distance on a wet runway, provided the requirements of paragraph (e) of this section are met.]"
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Starlionblue
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RE: Reversers In Landing Calculations

Sun Jan 29, 2006 1:41 am

Quoting Airfoilsguy (Reply 5):
Also, why have thrust reversers if the FAA, in essence, says they are not needed?

They may not be needed for max stopping distance, but pilots very often want to to make some turnoff before the end of the runway. So they are useful for normal operations.

Quoting FredT (Reply 16):
(2) May be included as an additional means of deceleration using recommended reverse thrust procedures when determining the accelerate-stop distance on a wet runway, provided the requirements of paragraph (e) of this section are met.]"

See! They may be used for calculations on wet runways in some cases.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
FDXmech
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RE: Reversers In Landing Calculations

Sun Jan 29, 2006 3:13 am

There's something I'm not getting here.

FAR 25.109 is Accelerate-stop distance. This FAR is for a rejected takeoff. Why would thrust reversers be figured in to supplement takeoff stopping distance when there is a good probability the takeoff was rejected because of an engine failure? As Cosmic Cruiser wrote, "Consider a rejected t/o due to an eng. failure, now you're stopping without all your reversers."
You're only as good as your last departure.
 
FredT
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RE: Reversers In Landing Calculations

Sun Jan 29, 2006 6:11 am

My bad. Good catch, FDXMECH. For landings, FAR 25.125 applies.

" (3) Means other than wheel brakes may be used if that means--
(i) Is safe and reliable;
(ii) Is used so that consistent results can be expected in service; and
(iii) Is such that exceptional skill is not required to control the airplane.
(c) For seaplanes and amphibians, the landing distance on water must be determined on smooth water.
(d) For skiplanes, the landing distance on snow must be determined on smooth, dry, snow.
(e) The landing distance data must include correction factors for not more than 50 percent of the nominal wind components along the landing path opposite to the direction of landing, and not less than 150 percent of the nominal wind components along the landing path in the direction of landing.
(f) If any device is used that depends on the operation of any engine, and if the landing distance would be noticeably increased when a landing is made with that engine inoperative, the landing distance must be determined with that engine inoperative unless the use of compensating means will result in a landing distance not more than that with each engine operating."

That could be interpreted as requiring dealing with the dead stick landing case, meaning no thrust reversers allowed to calculate the landing distance. Having to deal with the worst-case scenario with one engine inoperative is more likely. In that case, you still have to convince the certifying authorities that with most critical (for slowing down) engine inop, it is still "safe and reliable" and that "exceptional skill is not required to control the airplane".

You did remember to send your local FAA representative a nice christms gift this year, didn't you?

Oh, and as for counting in reversing on a RTO, you have to convince them that your proposed means of slowing down is safe and reliable and does not take exceptional skill in that case as well. The risk of a double engine failure on take-off is small, so you can probably argue that the one engine operative case is "safe and reliable". Then to prove that it does not require exceptional skill...

If they did pull that off for the -700, I would have liked to listen in on the discussion with the FAA!

[Edited 2006-01-28 22:16:24]
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IAHFLYR
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RE: Reversers In Landing Calculations

Sun Jan 29, 2006 10:28 am

Oh those FAA aircraft cert kids. Big grin
Any views shared are strictly my own and do not a represent those of any former employer.
 
bond007
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RE: Reversers In Landing Calculations

Mon Jan 30, 2006 8:52 am

Quoting Starlionblue (Reply 17):
See! They may be used for calculations on wet runways in some cases.



Quoting FDXMECH (Reply 9):
Quoting IAHFLYR (Reply 8):
Landing data is based on BRAKES only!

Takeoff data also.



Quoting Starlionblue (Reply 3):
They may sometimes be used in certain wet runway circumstances.

Guys, apart from maybe the 737 exception above, the regs say that they are not used in calculating LANDING distance. The exception for when they can used on wet runways is for TAKEOFF ... the initial question was for landing.

Accelerate-stop distances are used in takeoff calculations.


Jimbo
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bri2k1
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RE: Reversers In Landing Calculations

Mon Jan 30, 2006 9:27 am

Here's a question. What if the -700 is providing calculated stopping distance, taking into account all available information, and not minimum stopping distance given certain other factors? We're rarely going to stop in the bare minimum possible distance anyway, it would drive the passengers nuts if nothing else. I have no idea of the answer, but I think there is a difference between maximum performance stopping distance, shown in the performance charts, and probably used to determine if a particular runway is safe for landing, and then actual landing distance calculation.
Position and hold
 
Okie
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RE: Reversers In Landing Calculations

Tue Jan 31, 2006 2:47 am

Here is a little fuel for the fire.

On board laptop performance computers (OPC) were used in the WN Midway accident calculated for use of the T/R's on contaminated runway.

NTSB says not anymore.

Also states the the 700's were allowed credit when 300's were not
http://www.ntsb.gov/Pressrel/2006/060127.htm

Okie

[Edited 2006-01-30 18:51:30]
 
FDXmech
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RE: Reversers In Landing Calculations

Tue Jan 31, 2006 12:59 pm

I've been doing some research into this while at work. Researching the MEL's, inputting some APLC scenarios,etc.

Dry runway accelerate - stop distance not affected by one T/R inop.

Wet runway accelerate - stop distance not affected by one T/R inop.

Runways affected by clutter do have a hefty weight penalty with one inop T/R.

Yet reading various company publications leads me to believe that computed RTO stopping distances are never calculated with reverse thrust as an added braking component, regardless of runway condition, but simply a hidden, REQUIRED pad. In other words, when determining RTO stopping distance on a contaminated runway, brakes will determine the stopping distance, but having all reversers serviceable is a prerequisite to utilizing those numbers (required pad). Though the T/R's aren't figured in to get those numbers, without them, you couldn't legally use them.
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FDXmech
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RE: Reversers In Landing Calculations

Wed Feb 01, 2006 7:54 am

Quoting FDXMECH (Reply 24):
Runways affected by clutter do have a hefty weight penalty with one inop T/R.

Further research makes me qualify this statement. Certain aircraft in our fleet have a performance penalty when taking off on a cluttered runway with a T/R inop, some don't.

Older aircraft such as the 727 and DC10 do in fact have performance degradations on a cluttered runway with an inop reverser.

Others such as the MD11 & A300/A310 have none.

This leads me to think, why?
Certainly not because of reliability issues on the MD11 or A300 reverser. They are much more reliable than the DC10's. And certainly not the lack of attainable reverse thrust to decrease the stopping distance.

My theory is the more sophisticated anti-skid systems on the newer jets allowing the T/R's to be a "free" pad on stopping distance rather than an active component in this calculation.
You're only as good as your last departure.
 
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Starlionblue
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RE: Reversers In Landing Calculations

Wed Feb 01, 2006 8:54 am

Quoting FDXmech (Reply 25):

My theory is the more sophisticated anti-skid systems on the newer jets allowing the T/R's to be a "free" pad on stopping distance rather than an active component in this calculation.

Exactly. Those brakes are so good it's scary. Also braking calculations have a 50% pad. That is, if you maxed out the braking action you could brake in 2/3 of the distance you calculated as "minimum".

Of course, all the pax would break their noses on the IFE screens but that's another matter.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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