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convair880mfan
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Joined: Fri Jun 25, 2021 12:33 am

MD-90 better at hot and high airports than the B757?

Wed Aug 25, 2021 4:01 pm

I was looking at data from the Boeing webpage* on required takeoff runway requirements of various aircraft.

This document is not for pilots but for airport planners, but it seems like the MD-90 is a better performer at hot and high airports than the the Boeing 757-200. I took airports at an altitude of 6000 feet above sea level as a comparison point. [Boeing doesn't provide linear data for airports at an elevation of 5000 ft asl and says one cannot extrapolate from the tables it provides. There are many caveats on data . . . zero wind, zero runway slope, packs off et cetera.

The data are not completely comparable since the MD-90 data is for standard day + 15C while the Boeing 757-200 data is for standard day + 14C.
The Boeing aircraft seems limited by design takeoff weight, maximum brake energy and tire speed limits but not the MD-90. [By the way, what is the Fahrenheit total for standard day 6000 ft. asl + 14 C?

It doesn't seem like the 757 can takeoff at its maximum design takeoff weight while the MD-90 can at 6000 ft asl on hot days [standard day + 14 or 15C]. I always thought the Boeing 757-200 was the best performer for hot and high airports but now I am not so sure. Can anyone clear this up for me? Maybe I am comparing apples and oranges since the B757-200 is heavier. Thanks for any insights?

_________________
"Boeing Airport Compatability" Airplane Characteristics for Airport Planning. http://www.boeing.com/commercial/airpor ... nuals.page
 
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Florianopolis
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Re: MD-90 better at hot and high airports than the B757?

Wed Aug 25, 2021 10:08 pm

Yeah, but how much is each carrying how far? Maybe the 757 is below it's max payload but is it still carrying more farther than the maxed-out MD-90?
 
GalaxyFlyer
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Joined: Fri Jan 01, 2016 4:44 am

Re: MD-90 better at hot and high airports than the B757?

Wed Aug 25, 2021 10:44 pm

The real answer—it depends. No operator buys a plane on theoretical performance. The look at what their planned loads will be ; the range required and the local environmental conditions. They don’t buy the maximum performance but what they need, unless it corporate jet and a HNWI wants bragging rights that he can fly non-stop around the world while boarding at PBI to fly to TEB.

A big factor is the B757, as it would be operating at a lower percentage of the weight limits, can always beat the MD-90 carrying an MD-90 load.
 
GSOtoIND
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Re: MD-90 better at hot and high airports than the B757?

Wed Aug 25, 2021 10:47 pm

The difference is that the 757 at MTOW is carrying ~20% more passengers ~75% further than an MD90 at MTOW.
 
convair880mfan
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Re: MD-90 better at hot and high airports than the B757?

Wed Aug 25, 2021 11:43 pm

But it seems like the 757 with all that extra weight and all those extra passengers and all that extra range does not have the same short field performance as an MD-90 on a hot day at 6000 ft.asl

I realize the 757 is a bigger, heavier, longer-range and greater capacity aircraft. That's pretty obvious just from looking at the two next to each other at gates.

I live in a city where the airport is one mile above sea level. Back in the day one could watch the boarding area of various jetliners, take an elevator upstairs to a viewing area and watch those plane take off on the 13,000+ foot runway.

I'd see a Delta MD-90 with an overflowing boarding lounge empty into the airplane and an Eastern 757-200 with a fully crowded boarding area empty out and into the plane. Going to the viewing area I would watch as the MD-90 become airborne on the hottest days in July after a very short takeoff run. The Eastern 757-200 would be eating up a whole lot of runway before it became airborne.

Of course I don't know the exact number of passengers or payload of either, but when I looked at the Boeing performance charts it seemed like they backed up what I was witnessing with my eyes. Of course, perhaps the Boeing was operating at a lower thrust setting to cut down on wear and tear on the engines.
 
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Boeing757100
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Re: MD-90 better at hot and high airports than the B757?

Wed Aug 25, 2021 11:55 pm

It heavily, heavily depends on many things like payload, trim settings, flap settings, thrust settings, temperature outside, and other factors, as the users above mentioned. The 757 and MD-90 serve different segments of the market, so I think it is not too fair to compare them. Obviously a full 757 with the same thrust setting as a full MD-90 would take up more runway because it is heavier and requires a higher V1 speed.

On the less mechanical side, the 757 and MD-90 are both great aircraft, but no one, ABSOLUTELY no one is better than our mighty 757. :smile:

And my reply might not be completely correct so anyone more knowladgable can correct me.
 
convair880mfan
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Posts: 253
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Re: MD-90 better at hot and high airports than the B757?

Thu Aug 26, 2021 12:02 am

:smile: I see what you're saying
 
johns624
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Re: MD-90 better at hot and high airports than the B757?

Thu Aug 26, 2021 1:13 am

convair880mfan wrote:

I'd see a Delta MD-90 with an overflowing boarding lounge empty into the airplane and an Eastern 757-200 with a fully crowded boarding area empty out and into the plane. Going to the viewing area I would watch as the MD-90 become airborne on the hottest days in July after a very short takeoff run. The Eastern 757-200 would be eating up a whole lot of runway before it became airborne.
Are you sure that your memory isn't playing tricks on you? Wiki shows the in-service date of the MD90 after Eastern had been bellyup for a couple of years.
 
LCDFlight
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Re: MD-90 better at hot and high airports than the B757?

Thu Aug 26, 2021 1:51 am

An airline's question would be, can both airplanes carry a 90-100% full passenger load on a given hot & high mission, like JAC-ATL in summer or something like this. It is not a range contest. Nor is it a size contest. Let's try to factor that out and just look at field performance.

Although yes, they are connected. JAC-ATL is going to put an M90 closer to MTOW than a 752. Maybe JAC-ORD is a fairer job that both aircraft should be able to do. The M90 might win that one. I suspect the 752 will win JAC-ATL because it has more excess MTOW which (I am assuming) translates to excess performance.
 
BoeingGuy
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Joined: Fri Dec 10, 2010 6:01 pm

Re: MD-90 better at hot and high airports than the B757?

Thu Aug 26, 2021 6:02 am

This thread is all a moot point. No MD-90s remain in service. The last MD-90 was withdrawn from service over a year ago.

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