Flight delays / cancellations due to heat?

OK, I will admit to a small understanding of heat affecting air density relative to lift as it applies to aircraft, however.....when the national news reports that flight delays are due to high temps in the western US, I have to ask myself how we managed to support our military logistics in the middle east with any reasonable expectations when the temps are high? Is the media reporting this heat story out of context, or how have we been sustaining commercial air operations? Anyone care to chime in here as to how UPS, FedX, and all the other carriers handle this?

 

After diligent work on the idiot wheel, lighter loads, longer take offs, shallower climbs, higher approach speeds, a lot of inhaling, and sweat...swet. Also delicate touch on the controls. Bad numbers coming off the idiot wheel, shut it down and call it a day.

 

Most military aircraft are overpowered, especially if you do not load them up fully, and designed to run in pretty foul conditions. Many of the airfields in SWA are also very long to allow for the typically hot weather. Taif, Saudi Arabia, where I flew, was at 4800', but the military runway there was 12,000' long, so no problem on summer take-offs.

High temperatures, high pressure, and low humidity adversely affect density altitude, which affects lift on take-off. Same thing also lowers thrust, so you have fewer lifties and fewer thrusties, to put it in technical terms.

Here in Albuquerque at 5300', high temperatures can lead to density altitudes of over 9000'. Like Wednesday with 105 F, 30.41" mercury, and 5% relative humidity. The old 727s had to shut off anything using bleed air on take-off in the summer here. They could not spare the thrust. Made for a warm cabin until you cleared the mountains.

A-10 single engine testing was done at Cannon AFB, NM during one of the summers I was there. At 4295' elevation, summer density altitudes often reached 8000'. Climb rate was miniscule on the A-10 with a load at that density altitude. In real life, might have meant jettisoning stores and dumping fuel to keep her flying.

 

birds won't fly either if it gets too hot...

 

It wouldn't surprise me if flight delays were due to problems with ground ops rather than anything flying related. The luggage throwers and other ground folks probably have something in their contracts regarding work/rest cycles during high heat. An unexpected heat wave means they are, for practical purposes, trying to run with reduced manning.

As for how the military does it..... Well unlike civilian employees who can quit if you try and work them to death in the heat the military sometimes just has to work through it. I have been shoulder deep in the hot engine cowlings trying to get a bolt loose to remove a faulty generator so we can get the hell out of some nasty cooking hot field in Iraq. The military does take the heat thing fairly seriously though and there are lots of rules when deployed of at home station. There are work/rest cycles in an air conditioned area. There are also portable A/C carts the size of trucks that can be used to blow cold air over a work area or inside a plane during preflight.

 

Then there's Quito, Ecuador. Elevation is very close to 10,000 ft. ASL to begin with. On the Equator (hence the name of the country) it's also pretty warm.

Some planes, like the aforementioned old 727 could not be used there.

 

Another problem in extreme heat is that most transport category aircraft only have performance data up to 50 degrees C. If the temperature goes above that, you can't go because you have no performance data.

I don't know if it has gotten that hot, however.

 

Talked about here as well...

Too HOT For RJ's IN PHX — Civil Aviation Forum | Airliners.net

 

Actually the performance data is up to the airline. The bigger the performance window the more the cost. With the same environmental conditions with the same model of airplane with the exact same load airline X might not be able to go while airline Y can. This is because airline Y paid more money.

 

Thanks to all for the replies! The civil aviation blog link really helped...and a special thanks to Mr. Parks for his informative and very humorous response!! You gotta love the way he gets his personal touch in his info...

 

Really? I guess I should not be surprised. Boeing will do pretty much anything if you are a large enough customer. I would imagine it is hard to collect data above 50C consistently, though.

Have you seen airplanes with performance data above that? What is the highest you have seen?

 

Having a difficult time believing that...

Any evidence?

 

So do I given that the FAA is very involved in assigning an aircraft it's limitations.


Mark

 

performance data manipulations or not, anyone that has flown at heavy weights in high heat enviornmental conditions knows that they are at the limits of the airplane... it's all in the numbers, when they don't "add up" it is definitely a no go... one can't manipulate performance... the numbers are very slow to appear, the runway gets very short, climb rate is gone...
essentially the plane is very close not wanting to fly... regardless of what has been published, there is a point where the pilots won't go... bribes cannot increase performance windows

 

I've not heard of it for temperature, but I have heard of it for other limitations, like maximum takeoff altitude.

Most transport category airplanes have a limitation of 10,000 feet for takeoff. This works fine in North America, where there are no airports higher than 10,000 feet. However, Quito Ecuador is at 14,000 feet.

Some manufacturers have created a service bulletin which raises the maximum takeoff altitude. To do this, they had to do some additional flight testing, and in some cases make a minor modification to the pressurization system.

If you want to go legally from Quito, you have to pay the manufacturer for the service bulletin and whatever minor physical mods you need, and presto, you are good.

I'm sure they could do the same thing for temperature limitations, although I've never seen it.

Gulfstream has an issue with the GIV where it is Category D for approaches. This means higher weather minimums at certain airports, or in some cases the inability to do an instrument approach at all-- Aspen, for example.

However, the approach category is a function of the stall speed at the maximum landing weight. If you lower the maximum landing weight on a GIV, you can get the stall speed low enough that it's now Category C.

So, Gulfstream came out with a service bulletin which allows you to lower the maximum landing weight, and presto, Category C. In the old days, you could change a placard (even in flight, according to some operators), and be good. Now they require a logbook entry to switch back and forth.

None of this has anything to do with how the aircraft actually performs.

 

Every airline and every aircraft type have runway performance numbers for every runway they use. The basic numbers provided by the airframer/engine people usually only go to 50C, but I've seen maximums at 45C. So, if you don't have the data you have two choices, don't go, or buy the data from Boeing or Airbus. If you are USair (formerly AmWest) based in PHX you probably already have the data. If your airline is based in a cooler airport maybe you don't.

 

Bob, don't you also have an absolute limitation?

The Learjet 35, for instance, has an absolute limitation of 50C. It's not a function of performance data-- it's right there in the Limitations section of the AFM.

 

Boeing or Airbus can provide performance data for any temp/altitude/runway/engine an operator wants. You want to fly a 747 out of a 5,000' runway in the Andes? They will get you the data (you may not like it!).

I'm sure Lear will do the same.

 

It isn't a question of performance data (well, not directly). The Limitations section has a limitation in it. To change the limitation would require a service bulletin, or an STC.

Specifically, an internet search shows that the CRJ-200 has a limitation of ISA+35 for takeoff (which would be equal to 50C at sea level).

Usually, this has to do with tire issues.

Again, it is not a question of performance. Maybe you could get at STC for different tires, or something, I don't know.

 

We are talking about take off performance. Aircraft have for years performed TO's with temp over 50C. All you need is the manufacture to give you the numbers. If you don't have performance data you can not take off on any runway regardless of temp. You don't need an STC, you need data.

 

No, we're not talking about takeoff performance. Maybe you are, but I'm not. I'm talking about a LIMITATION. In the case of the CRJ-200, the LIMITATION is ISA+35. Doesn't matter about performance.

Can you get the limitation changed? Maybe, I don't know.

 

I don't have a CRJ manual here. But, I can tell you each airline that uses them have a different limitation section depending on what they need. Maybe Bombardier didn't come up with numbers to certify beyond 50C and therefore that's the limit.

 

This is what I was trying to explain and I think you did a much better job than I did.