madog
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Reverse Thrust Usage

Sun Jul 15, 2012 1:45 pm

Perhaps pilots and airline operation employees can help answer my question.

On some airlines I travelled in the previous few years, such as Singapore, Cathay, EVA Air, upon touchdown, I noticed that judging by the lack of reverse thrust spooling noise, that minimum reverse thrust (idle perhaps?) are used. On the other hand, other airlines such as QANTAS, and airlines in China (Air CHina, China Eastern, CHina Southern, Hianan to name a few) use evidently (again judging by the noise) reverse thrust to slow the aircraft down on roll out.

I'm guessing that, if the use of minimum reverse thrust is to minimise engine wear and it's an operational thing depending on the airline?
 
tdscanuck
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RE: Reverse Thrust Usage

Sun Jul 15, 2012 4:57 pm

Quoting madog (Thread starter):
I'm guessing that, if the use of minimum reverse thrust is to minimise engine wear and it's an operational thing depending on the airline?

It's an operational thing to balance noise, engine wear, thrust reverser wear, and brake wear. Policies vary wildly.

Tom.
 
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larshjort
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RE: Reverse Thrust Usage

Sun Jul 15, 2012 6:46 pm

I believe it is not legal to use T/Rs above idle in CPH unless in an emergency because of noise issues.

/Lars
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Mir
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RE: Reverse Thrust Usage

Sun Jul 15, 2012 10:31 pm

Quoting Larshjort (Reply 2):
I believe it is not legal to use T/Rs above idle in CPH unless in an emergency because of noise issues.

I don't know about illegal, but many airports in Europe publish notices to pilots that reverse thrust should not be used above idle due to noise, unless operationally required.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
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zeke
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RE: Reverse Thrust Usage

Sun Jul 15, 2012 11:32 pm

Quoting madog (Thread starter):

Couple of considerations.

Reverse thrust typically does not reduce the stopping distance these days, on an aircraft like an A330 they decelerate at the rate the pilots select auto brake. All reverse thrust does is changes the amount of brake pressure being applied, the deceleration rate is still the same with auto brake idle reverse or full reverse.

Carbon brakes as found on airliners these days wear mainly in proportion to the number of brake applications, a nice long single application by the auto brakes is the preferred way to treat them. They also work best when warmer.

We will use reverse if the runway is contaminated, wet, or with a tailwind. At CX full reverse thust is the normal procedure, idle reverse is a normal consideration if operationally feasible, our landing distance calculations are based up no reverse.
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Thai744
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RE: Reverse Thrust Usage

Mon Jul 16, 2012 8:09 am

Silly questions and slightly off topic, however just in relation to zeke's post above... how much tailwind can an aircraft actually land with? What's the maximum amount of wind permissible and does it vary between aircraft types?
 
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zeke
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RE: Reverse Thrust Usage

Mon Jul 16, 2012 9:29 am

Quoting Thai744 (Reply 5):
how much tailwind can an aircraft actually land with? What's the maximum amount of wind permissible and does it vary between aircraft types?

The maximum will be an aircraft limit, and does vary with type. On the A330 for example it is 15 kts.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
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Faro
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RE: Reverse Thrust Usage

Mon Jul 16, 2012 10:50 am

Quoting zeke (Reply 6):
Quoting Thai744 (Reply 5):
how much tailwind can an aircraft actually land with? What's the maximum amount of wind permissible and does it vary between aircraft types?

The maximum will be an aircraft limit, and does vary with type. On the A330 for example it is 15 kts.

What is this figure based on? Given an infinite runway, would there still be a limiting tailwind component?


Faro
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tdscanuck
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RE: Reverse Thrust Usage

Mon Jul 16, 2012 11:18 am

Quoting faro (Reply 7):
What is this figure based on? Given an infinite runway, would there still be a limiting tailwind component?

At some point you'll hit the limit of what the tires (tire speed) and brakes (kinetic energy) can handle. The performance of both relates directly to groundspeed at touchdown, so if you get enough tailwind you'll run into one of those limits. Most likely tire speed first, because the limiting condition for brakes is usually rejected takeoff at MTOW, but high tail winds are going to drive you towards hot brakes.

Tom.
 
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zeke
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RE: Reverse Thrust Usage

Mon Jul 16, 2012 11:46 am

Quoting faro (Reply 7):

What is this figure based on? Given an infinite runway, would there still be a limiting tailwind component?

I think all FAR/JAR 25 aircraft automatically get 10 kt, anything above that needs to be flight tested to 150% greater than the limit, so to get 15 kt, they have to test to 22.5 kt. They need to have landing data for the tailwind.

The highest tailwind component I am aware of for a FAR/JAR 25 aircraft would be something like a DHC-7 that would be 20 kts, ATR-42, Airbus A319/20/21/A330/A340, Boeing 737/747/757/767/777, BAe 146/RJ family are all capable of 15 kts.

Practically the limit would be rate of descent, airlines do not like to see descent rates in excess of 1000 fpm on final, and that is what you may need to do with a high ground speed to maintain the glideslope.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
bond007
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RE: Reverse Thrust Usage

Tue Jul 17, 2012 2:37 am

Quoting zeke (Reply 4):
Reverse thrust typically does not reduce the stopping distance these days, on an aircraft like an A330 they decelerate at the rate the pilots select auto brake. All reverse thrust does is changes the amount of brake pressure being applied, the deceleration rate is still the same with auto brake idle reverse or full reverse.

I know you did mention it later, but to be clear to other folks, that is only correct for dry runways ... where it provides little to no difference. On a contaminated runway, especially slush, it will reduce the stopping distance of course.


Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
tdscanuck
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RE: Reverse Thrust Usage

Tue Jul 17, 2012 3:04 am

Quoting bond007 (Reply 10):
I know you did mention it later, but to be clear to other folks, that is only correct for dry runways ... where it provides little to no difference. On a contaminated runway, especially slush, it will reduce the stopping distance of course.

That's only true if the autobrakes hit their braking decelleration limit (i.e. they have to let off to prevent the wheels from locking up). As long as the wheels aren't skidding, the airplane will apply as much brake as it needs to to reach the autobrake decelleration threshold and no more. Since it's a deceleration, the landing distance won't change unless the thrust reveser + brake combination can't actually reach the requested decelleration.

Tom.
 
bond007
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RE: Reverse Thrust Usage

Tue Jul 17, 2012 3:21 am

Quoting tdscanuck (Reply 11):
As long as the wheels aren't skidding

Right, which is why I mentioned slush. The QRH will show reduced landing distance in most cases on slush, compacted snow, and ice with T/Rs as opposed to brakes alone.


Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
bond007
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RE: Reverse Thrust Usage

Tue Jul 17, 2012 4:26 am

Quoting madog (Thread starter):
I'm guessing that, if the use of minimum reverse thrust is to minimise engine wear and it's an operational thing depending on the airline?

Also, this is a common topic. Most things posted in this thread have probably already been covered in the 'similar topics' list at the bottom of the page  

Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!

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