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737NG Vs MD80 Landing Performance  
User currently offlineDFWHeavy From United States of America, joined Jul 2011, 560 posts, RR: 0
Posted (1 year 5 months 2 weeks 1 day 14 hours ago) and read 6355 times:

Hello everyone,

I'm sitting at the United Club at SAT killing some time before my AA flight. While watching several AA and WN planes land, it seems that each of the AA MD80s has a longer landing/roll out than the WN 737s.

Now I know a lot of factors can affect this, but it seems to be the case that every AA plan I've seen comes in a bit hotter and takes longer to stop.

In general, does the 737NG have better landing performance than the MD80? If so, does anyone have any numbers to demonstrate the differences in a given situation?

Thanks!


Christopher W Slovacek
22 replies: All unread, jump to last
 
User currently offlineRoseflyer From United States of America, joined Feb 2004, 9661 posts, RR: 52
Reply 1, posted (1 year 5 months 2 weeks 1 day 14 hours ago) and read 6302 times:

Quoting DFWHeavy (Thread starter):

I'm sitting at the United Club at SAT killing some time before my AA flight. While watching several AA and WN planes land, it seems that each of the AA MD80s has a longer landing/roll out than the WN 737s.

I think what you are seeing is different use of the Autobrake and different SOP. The 737 has 3 different autobrake settings (other than rejected takeoff) for different deceleration rates. With 8,500 ft of runway, the pilot can choose how much brake he wants to use.

I don’t know how WN and AA have their SOP, but using a lower autobrake setting saves tire and brake life. Not all of the AA MD80s even have autobrakes since it is an option and TWA and RenoAir did not have that option.

In the case of SAT, neither the MD80 nor 737 will be landing anywhere near max braking capability. Both can easily stop short of 5,000 ft, but doing so tears up the tires, which is costly for the airline.



If you have never designed an airplane part before, let the real designers do the work!
User currently offlineDFWHeavy From United States of America, joined Jul 2011, 560 posts, RR: 0
Reply 2, posted (1 year 5 months 2 weeks 1 day 14 hours ago) and read 6262 times:

Thanks for the insight Roseflyer.

Indeed SAT is using the 8500 ft runway and I know that is plenty long. I was just a little surprised that every flight I've seen so far (and I know it's by no means scientific), has the WN stopping quicker/shorter than the AA flights.



Christopher W Slovacek
User currently offlineRoseflyer From United States of America, joined Feb 2004, 9661 posts, RR: 52
Reply 3, posted (1 year 5 months 2 weeks 1 day 14 hours ago) and read 6233 times:

Quoting DFWHeavy (Reply 2):

Indeed SAT is using the 8500 ft runway and I know that is plenty long. I was just a little surprised that every flight I've seen so far (and I know it's by no means scientific), has the WN stopping quicker/shorter than the AA flights.

It is probably because the AA flight manual has their pilots using a lower autobrake setting. WN is known for valuing fast turn around times, so it wouldn’t surprise me if their flight manual allowed for higher autobrake settings (assuming they use the autobrake), if it reduces taxi time. WN has a reputation for taxing fast.



If you have never designed an airplane part before, let the real designers do the work!
User currently offlineokie From United States of America, joined Jul 2003, 3065 posts, RR: 3
Reply 4, posted (1 year 5 months 2 weeks 1 day 8 hours ago) and read 5848 times:

Quoting DFWHeavy (Thread starter):
Now I know a lot of factors can affect this, but it seems to be the case that every AA plan I've seen comes in a bit hotter and takes longer to stop.

I am not familiar enough with SAT to say but many times the braking involved has to do with which taxiway they plan to use to get to that companies gate location. No sense using a lot of brake if you need to go another 1500 ft to get to the taxiway that you will need to get to the gate.

Here at KOKC if WN lands on 17L/35R 9802ft they tend to brake pretty hard to make taxiway G right at mid field which pretty much exits onto the ramp area via K directly in front of their gates. If they operate on 17R/35L they seem to brake normally since they are going on a tour of the taxiways until they get close to their gate before the controllers let the planes get onto the ramp area.

Just the opposite happens with AA, UA, DL, F9 etc as they are on the other end of the terminal.
Just some food for thought that taxiways and runway can play into the picture as well.

Quoting DFWHeavy (Thread starter):
AA MD80s has a longer landing/roll out than the WN 737s.

Just a general observation with no facts but here it seems that DL's MD80's tend to roll way longer but that can be the airlines SOP on brake setting and how much farther they have to go to get to a taxiway.

Okie


User currently offlineatct From United States of America, joined Mar 2001, 2298 posts, RR: 38
Reply 5, posted (1 year 5 months 2 weeks 11 hours ago) and read 5661 times:

AA is notorious for rolling to the end to save on break life. They've sent many an airplane around because they wont exit at the high speed or get on the brakes.


"The way to get started is to quit talking and begin doing." - Walt Disney
User currently offlineTrijetsRMissed From United States of America, joined Oct 2006, 2364 posts, RR: 7
Reply 6, posted (1 year 5 months 6 hours ago) and read 4923 times:
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For the past 2-3 years, AA's procedure has dictated that pilots use little to no reverse thrust on S80 landings, whenever possible. This factors into a longer landing roll. I do not know for certain if it is a fleet-wide SOP, or specific to the MDs.


There's nothing quite like a tri-jet.
User currently offlineAA737-823 From United States of America, joined Mar 2000, 5848 posts, RR: 11
Reply 7, posted (1 year 4 months 4 weeks 1 day 8 hours ago) and read 4704 times:

Quoting TrijetsRMissed (Reply 6):
This factors into a longer landing roll.

No it doesn't.
Not if they've got autobrakes in use, at least.
The autobrake targets a specific DECELERATION RATE. If you apply reverse thrust, the autobrake will still target the same RATE of decel, so it actually eases off of the brakes. More reverse thrust? Less wheel brake. Less or idle reverse? Lots of wheel brake. That's why, as a passenger, you rarely "feel" the effects of reverse thrust. Unless, of course, the crew has opted for manual braking!

I suspect AA's habit has to do with reducing fuel consumption of the incredibly hungry JT-8's.


User currently offlineTrijetsRMissed From United States of America, joined Oct 2006, 2364 posts, RR: 7
Reply 8, posted (1 year 4 months 4 weeks 1 day 4 hours ago) and read 4660 times:
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Quoting AA737-823 (Reply 7):

Quoting TrijetsRMissed (Reply 6):
This factors into a longer landing roll.

No it doesn't.
Not if they've got autobrakes in use, at least.
The autobrake targets a specific DECELERATION RATE

I beg to differ based on my experience. And yes, I know what a DECELERATION RATE is...thank you.

I recently flew STL-ORD, landing on 14R. We used nearly the entire runway, (13,000 ft length), for our landing roll; pulling off at the final taxi exit. Reverse thrust was not engaged. I have been on many, (HUNDREDS), of MD-80 landings where reverse thrust was applied and the roll was well below 5,000 ft, (approximating).

Quoting AA737-823 (Reply 7):
I suspect AA's habit has to do with reducing fuel consumption of the incredibly hungry JT-8's.

You don't say...   That said, I don't think AA want to burn through the wheel brakes either.  
Quoting AA737-823 (Reply 7):
Less or idle reverse? Lots of wheel brake.

Clearly the rate of deceleration has been adjusted to compensate for the non-reverse thrust procedure.



There's nothing quite like a tri-jet.
User currently offlineRoseflyer From United States of America, joined Feb 2004, 9661 posts, RR: 52
Reply 9, posted (1 year 4 months 4 weeks 16 hours ago) and read 4509 times:

Quoting TrijetsRMissed (Reply 8):
I beg to differ based on my experience. And yes, I know what a DECELERATION RATE is...thank you.

I recently flew STL-ORD, landing on 14R. We used nearly the entire runway, (13,000 ft length), for our landing roll; pulling off at the final taxi exit. Reverse thrust was not engaged. I have been on many, (HUNDREDS), of MD-80 landings where reverse thrust was applied and the roll was well below 5,000 ft, (approximating).

AA737 was right, but you may be right too. The automatic brake system on the MD-80 selects a deceleration rate (Min, Med, Max). Using reverse thrust does not shorten the brake distance when the autobrakes are used. If autobrakes are applied and reverse thrust is used, it only decreases brake wear.

A couple things may explain your differences in experiences. First off, the ex-TWA or ex-Reno Air MD80s do not have Autobrakes. It was a customer option on the MD80 and TWA and Reno Air did not select that option, so you may have been on an airplane with no autobrakes.

Secondly there are different brake rate options. You may experience them selecting different options for brake deceleration. If they are choosing the MED setting, then reverse thrust will help save brake life and allow a shorter turn. The deceleration rates are 4 ft/sec^2, 6.5 ft/sec^2 or full brake pressure modulated by the anti-skid to avoid skidding tires. Even at 4 ft/sec^2, you would never take 13,000ft of runway, so the pilot was modulating pressure with his feet in that instance.

If autobrake MIN or MED is selected, reverse thrust has no impact on brake length. If it is not selected or is on MAX, then reverse thrust matters. Not using reverse thrust does not necessarily mean longer landing roll.



If you have never designed an airplane part before, let the real designers do the work!
User currently offlinemandala499 From Indonesia, joined Aug 2001, 6897 posts, RR: 76
Reply 10, posted (1 year 4 months 3 weeks 6 days 23 hours ago) and read 4362 times:

FAR Landing Runway length requirements:
MD80, full flaps, sea level, 149500lbs landing weight, max manual brakes, no reverse: 1500 meters.

737-800W, full flaps, sea level, 146300lbs landing weight, max manual brakes, no reverse: 1675 meters.

The actual requirement would be 0.66 of those numbers...

Quoting Roseflyer (Reply 9):
AA737 was right, but you may be right too.

They're both right. The actual landing roll length has a lot to do with the conditions of the day, policy, and crew discretion... the landing roll required, well, different story.

Manual braking with no reverse is going to be longer than manual braking with reverse, with the same landing weight, same conditions, same brake pressure applied.

Auto-brake MAX with reverse for the same conditions will probably result in shorter roll.

Auto-brake MIN with reverse will only be shorter if the deceleration effect of the reverser is greater than the A/B MIN decel rate.

Quoting atct (Reply 5):
AA is notorious for rolling to the end to save on break life. They've sent many an airplane around because they wont exit at the high speed or get on the brakes.

Steel brakes?   
Won't matter on carbon brakes...

Quoting Roseflyer (Reply 3):
It is probably because the AA flight manual has their pilots using a lower autobrake setting. WN is known for valuing fast turn around times, so it wouldn’t surprise me if their flight manual allowed for higher autobrake settings (assuming they use the autobrake), if it reduces taxi time. WN has a reputation for taxing fast.

More braking = hotter brakes, and hot brakes take time to cool, brake too hard and you'd end up being delayed to cool the brakes more... unless you have some brake fans   

Mandala499



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlineRoseflyer From United States of America, joined Feb 2004, 9661 posts, RR: 52
Reply 11, posted (1 year 4 months 3 weeks 6 days 20 hours ago) and read 4338 times:

Quoting mandala499 (Reply 10):
Quoting atct (Reply 5):
AA is notorious for rolling to the end to save on break life. They've sent many an airplane around because they wont exit at the high speed or get on the brakes.

Steel brakes?
Won't matter on carbon brakes...

Most of AA's fleet doesn't have carbon brakes. The MD80 never had them. 737 only got them about 5 years ago. 757-200 and 767-300 did not have them until late in the production run (1999).

Their only planes with them are the 777s unless they have a mixed fleet.

[Edited 2013-05-07 07:59:44]


If you have never designed an airplane part before, let the real designers do the work!
User currently offlineAA737-823 From United States of America, joined Mar 2000, 5848 posts, RR: 11
Reply 12, posted (1 year 4 months 3 weeks 6 days 14 hours ago) and read 4280 times:

Quoting Roseflyer (Reply 11):
Most of AA's fleet doesn't have carbon brakes.

Lots of carriers haven't switched to carbon brakes, for whatever reason. Though I WISH mine would, because I'm tired of lugging/lifting/dropping brakes that weight several hundred pounds around. My joints and back don't care for them, either!

Quoting TrijetsRMissed (Reply 8):
And yes, I know what a DECELERATION RATE is...thank you.

I don't doubt that you knew what a deceleration rate was. But, be honest- did you know that the RATE is what the autobrake system targets, rather than a specific brake pressure psi or any of the other things that could be used?

Quoting TrijetsRMissed (Reply 8):
I recently flew STL-ORD, landing on 14R. We used nearly the entire runway, (13,000 ft length), for our landing roll; pulling off at the final taxi exit. Reverse thrust was not engaged. I have been on many, (HUNDREDS), of MD-80 landings where reverse thrust was applied and the roll was well below 5,000 ft, (approximating).

That's more theoretical/anecdotal evidence, rather than empirical. Reverse thrust would never shave 8,000 feet off of a landing roll, in the first place. And, you as a passenger (unless you were in the jumpseat) have NO WAY of knowing whether reverse thrust was engaged on an MD-80 anyway... if they engaged idle reverse, you won't hear the difference.
AND, we still don't know whether the plane you were on was even equipped with autobrakes, as RoseFlyer pointed out.

Quoting TrijetsRMissed (Reply 8):
Clearly the rate of deceleration has been adjusted to compensate for the non-reverse thrust procedure.

You've missed my point: that rate cannot BE adjusted. You're either in manual, or one of the autobrake detents.

Quoting TrijetsRMissed (Reply 8):
You don't say...   That said, I don't think AA want to burn through the wheel brakes either.  

Perspective shift: pilots at several carriers are recognized and rewarded for burning LESS FUEL than average; they are NOT rewarded for reducing brake wear. There is NO incentive for a pilot to "save the brakes" anymore.
Though, as the guy that changes brakes, I'd MUCH rather they used full reverse and kept their toes otherwise occupied!


User currently offlineTrijetsRMissed From United States of America, joined Oct 2006, 2364 posts, RR: 7
Reply 13, posted (1 year 4 months 3 weeks 3 days 10 hours ago) and read 4016 times:
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Roseflyer/mandala, thank you for adding your input.

Quoting AA737-823 (Reply 12):
But, be honest- did you know that the RATE is what the autobrake system targets, rather than a specific brake pressure psi or any of the other things that could be used?

I do understand. But perhaps I was not clear enough from last last point of my previous post on adjusting the rate. Perhaps I was remiss in leaving out the terms, MIN, MED, and MAX, and failing to acknowledge the difference between legacy AA vs TW MD-80s.

Quoting AA737-823 (Reply 12):
That's more theoretical/anecdotal evidence, rather than empirical.

True. I cited it as an example to illustrate my claim; not to show as hard evidence.

Quoting AA737-823 (Reply 12):
AND, we still don't know whether the plane you were on was even equipped with autobrakes, as RoseFlyer pointed out.

FWIW, the aircraft was N972TW.

Quoting AA737-823 (Reply 12):
You've missed my point: that rate cannot BE adjusted. You're either in manual, or one of the autobrake detents.

Some would say switching between MIN, MED, and MAX could be considered an adjustment.

Quoting AA737-823 (Reply 12):
Perspective shift: pilots at several carriers are recognized and rewarded for burning LESS FUEL than average; they are NOT rewarded for reducing brake wear. There is NO incentive for a pilot to "save the brakes" anymore.

Are you saying AA pilots are not advised, instructed, or encouraged to be mindful of brake wear? Not in the policy, SOP, training, foot notes, etc. Not at all?

I don't work for AA, but that would surprise me, considering their second largest fleet type does not have auto-brakes on 1/3 of the aircraft.

At least one local poster seems to think the contrary...

Quoting atct (Reply 5):

AA is notorious for rolling to the end to save on break life.



There's nothing quite like a tri-jet.
User currently onlineMax Q From United States of America, joined May 2001, 4556 posts, RR: 19
Reply 14, posted (1 year 4 months 3 weeks 3 days 6 hours ago) and read 3964 times:

Never flew the 737 but I did fly the MD80 for four years and it does have some disadvantages in stopping performance due to design.


If you actuate reverse after landing with too high a pitch attitude (nosewheel not on the ground) the lower half of the clamshell reverse buckets can actually hit the ground as their extending and extended activation arc will protrude beneath the lower rear fuselage.


At Cal our solution to this problem was to only allow reverse thrust after the nosewheel was on the ground. This is a significant delay in starting a significant part of deceleration devices. The B737 does not have this issue. Futhermore we had to be out of reverse by 100 knots due to FOD concerns !


This gave you a very small limited window for the use of reverse.


In addition to that, the MD80 brakes constantly vibrated with application and were generally weaker than any Boeing I have flown. Seems to be a Douglas trait as the DC10 brakes were weak as well.



The best contribution to safety is a competent Pilot.
User currently offlineTrijetsRMissed From United States of America, joined Oct 2006, 2364 posts, RR: 7
Reply 15, posted (1 year 4 months 3 weeks 3 days 5 hours ago) and read 3961 times:
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Quoting Max Q (Reply 14):
In addition to that, the MD80 brakes constantly vibrated with application and were generally weaker than any Boeing I have flown.

This is one thing MDC improved greatly with the MD-90.



There's nothing quite like a tri-jet.
User currently offlineCPDC10-30 From United Kingdom, joined Feb 2000, 4785 posts, RR: 23
Reply 16, posted (1 year 4 months 3 weeks 1 day 20 hours ago) and read 3779 times:

It's always fun at LHR when you'd get EI (and also formerly BD) braking very heavily when landing on 27R, so that they could taxi directly to the gates at T1  

User currently offlinebrons2 From United States of America, joined Sep 2001, 3015 posts, RR: 4
Reply 17, posted (1 year 4 months 3 weeks 7 hours ago) and read 3601 times:

Most rollouts on the MD-80 are long on AA that I have have experienced (and it's been a lot...) however the last time I flew AA into PDX (in 2009 I think it was) the pilot absolutely stood on the brakes. I was quite shocked at the force of the braking and it threw me forward into my seatbelt, as well as eliciting a few gasps out of the passengers. However it was soon appreciated as we took what must have been the very first taxiway and right onto our gate! I swear it couldn't have been more than 45 seconds from the time we touched down until we were at the gate! Amazing. I didn't know the MD-80 could stop that fast.

FWIW, we were traveling westbound when that happened and landed on the more southern of the two runways.



Firings, if well done, are good for employee morale.
User currently onlineMax Q From United States of America, joined May 2001, 4556 posts, RR: 19
Reply 18, posted (1 year 4 months 3 weeks 5 hours ago) and read 3582 times:

Quoting brons2 (Reply 17):
however the last time I flew AA into PDX (in 2009 I think it was) the pilot absolutely stood on the brakes. I was quite shocked at the force of the braking and it threw me forward into my seatbelt, as well as eliciting a few gasps out of the passengers. However it was soon appreciated as we took what must have been the very first taxiway and right onto our gate!

Really ? that's something worth appreciating !


How about a less violent landing roll and getting to your gate 3 minutes later ?


Not clever and very unprofessional, scaring passengers deliberately is inexcusable.



The best contribution to safety is a competent Pilot.
User currently offlineBarney Captain From United States of America, joined Nov 2001, 966 posts, RR: 13
Reply 19, posted (1 year 4 months 2 weeks 6 days 18 hours ago) and read 3526 times:

Quoting Max Q (Reply 18):
Not clever and very unprofessional, scaring passengers deliberately is inexcusable.

That's a pretty broad statement.

There's no way to know what other factors were at play and why this crew chose to expedite off of the runway. It's quite possible they were being very profesional.



...from the Banana Republic....
User currently offlinevikkyvik From United States of America, joined Jul 2003, 10048 posts, RR: 26
Reply 20, posted (1 year 4 months 2 weeks 6 days 15 hours ago) and read 3479 times:
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Quoting mandala499 (Reply 10):
Auto-brake MIN with reverse will only be shorter if the deceleration effect of the reverser is greater than the A/B MIN decel rate.

Out of curiosity, does anyone know if this is ever the case? Can full reverse provide a larger decel rate than MIN autobrake?

Obviously it may vary by type, but just curious for any general experience.



"Two and a Half Men" was filmed in front of a live ostrich.
User currently onlineMax Q From United States of America, joined May 2001, 4556 posts, RR: 19
Reply 21, posted (1 year 4 months 2 weeks 6 days 8 hours ago) and read 3431 times:

Quoting Barney Captain (Reply 19):


Quoting Max Q (Reply 18):
Not clever and very unprofessional, scaring passengers deliberately is inexcusable.

That's a pretty broad statement.

There's no way to know what other factors were at play and why this crew chose to expedite off of the runway. It's quite
possible they were being very profesional.
Quoting brons2 (Reply 17):
I was quite shocked at the force of the braking and it threw me forward into my seatbelt, as well as eliciting a few gasps out of the passengers.

Disagree,



The best contribution to safety is a competent Pilot.
User currently offlineasqx From United States of America, joined Jun 1999, 615 posts, RR: 0
Reply 22, posted (1 year 4 months 2 weeks 6 days 7 hours ago) and read 3412 times:

Quoting TrijetsRMissed (Reply 8):
I recently flew STL-ORD, landing on 14R. We used nearly the entire runway, (13,000 ft length), for our landing roll

14R/32L at O'Hare is 9,685 ft long according to the latest Airport Diagram from the FAA's website. Now, 10L/28R is 13,001 ft in length and is the longest runway at O'Hare.


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