Recently, my daughter was flying home from Colorado. The first leg of her trip was from Colorado Spings to Denver aboard a DeHaviland Dash-8. This is a very short flight and the Dash-8 spends its day running back and forth. When my daughter’s plane arrived, she and the other passengers boarded and the pilot said that the flight would be delayed more than an hour because the fuel was too hot. How does this happen? Why does the fuel temp matter? Was the plane going to blow up? (No, I don’t really believe the plane was about to blow up.)
There used to be a commercial that claimed it was “so hot, airplanes couldn’t fly,” and I’m almost certain we’ve discussed this in that context, but damned if I can find it on searching for it.
Phoenix, June 26, 1990.
But, to say that “planes couldn’t fly” is a bit of exaggeration. The air density charts had to be updated to include this extreme temperature - it took a few hours.
I found this through Google, but it doesn’t shed any light on the “fuel is too hot” notion:
I can imagine that at a certain point, the temperature creates a risk of volatilized fuel igniting in a partially empty tank or something.
Trivia: The SR-71 Blackbird, the fastest plane anyone will publicly admit to, uses its own jet fuel as coolant – the fuel flows through the skin of the plane during supersonic flight and conducts away heat from the skin so it doesn’t melt. That’s some seriously ballsy engineering.
Could it be an issue with vapor lock? I know on a lot of older model cars if the fuel lines got too hot the fuel would vaporize in the line and the fuel pump would quit working. But I haven’t heard of that problem in years so would assume that we now have the technology to work around that issue.
I know a guy who works on fighter jet avionics. These consume considerable power and thus must dissipate serious heat. And about the only way you can do this in a fast, high-flying aircraft is to use the fuel for cooling.
I met an Australian airline pilot who told a story of flying a 737 to Alice Springs one summer day. About 30 minutes out they checked the weather and learned that the ground temperature was 54 degrees C (129 degrees F). Having never encountered this before, he checked the flight manual and it confirmed what he’d recalled - the maximum temperature allowed for a landing was 52. So they turned around and headed back to Adelaide.
I think the limitation was due to some hydraulic consideration. He said he wasn’t a bit sorry to have missed being on the ground in that heat.
Most commercial large jets do that by utilising a FCOC (Fuel Cooled Oil Cooler). The oil lubricates and cools the components and is in turn cooled by the normally much colder fuel.
The fuel can also be used to lower the temperature of hydraulic fluid by passing it through heat exchangers in the fuel tanks.
All this suggests that overheated fuel is not that common since it is used so often as a cooling medium.
Pretty sure it has to do with the flashpoint of the fuel/vapor in the tank. We had a TWA800 discussion in Great Debates recently, and one of the leading contributors to the disaster was the plane sitting on the tarmac in relatively nice weather (70 degrees F or so, IIRC) but running the air conditioners. Well, the AC packs are located directly below the center fuel tank, and put out quite a bit of heat. The theory is that the air packs heated the vapor and what little jet fuel was left in the CWT (as most jets have empty tanks regularly) into “dangerous” territory. All that was needed was the initial spark, which came via a frayed wire. Then, boom.
TWA800 isn’t the only plane; there was one earlier than that in another country that exploded after running the AC packs on the ground. Can’t recall any more information than that, though.
(W.A.G.) It might also have something to do with the fuel viscosity, the various pumps and injectors being designed to work with a certain viscosity level.
Denver is unusual because of the altitude. When I chagned planes in Denver once, they delayed the flight and almost bumped some of us off, because they said it was too hot to carry a full flight. This seemed a little scary because it wasn’t like they were putting us on scales.
Can’t speak for the DeHavilland, but on modern fighters the fuel is a significant heat sink for cooling the airplane. It’s easy to keep the a/c and fuel cool in flight, but on the ground (especially in hot conditions) it can be hard to keep the fuel cool. Once the fuel reaches a certain temp, it is virtually impossible to keep the avionics cool and the a/c needs to shut down.
ETA: a/c means aircraft, not air conditioning
I have been in a similar situation on a puddle-jumper flight from St Louis Missouri to Springfield Missouri. In my case four people had to be bumped (and the plane took off with four empty seats). Too hot to fly with a full passenger list.
So how do they operate airports in places that are just really hot all of the time? There is an airport in N’Djamena, Chad. There are times of the year where 42 degrees is the average temperature. How do they do it?
They SHOULD be weighing people and aviation experts have been arguing to do just that for years…but lard ass passengers and their “defenders” have fought the actual weighing of passengers for years.
I just figured they had some way to weigh the plane, like sensors in the landing gear.
nope, they just assume everybody weighs:rolleyes: 165 lbs or something like that.
At least they finally got around to weighing the carry on stuff and checked baggage!
If you get on one of those small commuter planes, they will often shift passengers around at the last minute. I’ve seen it plenty of times. Weight and balance(distribution) is THAT critical.
It’s more to do with conservative safety regulations than any real risk of a crash. There’s a lot of built-in safety factors in any of these decisions, with legal enforcement behind them. The plane would almost certainly make it off the ground and safely to its destination with the extra passengers staying on board, or with a slightly uneven weight distribution. It might require a bit more skill or effort on the part of the pilots. Really, it would just cut into the safety margins for emergency situations. The slightly overloaded plane would still take off, but if it had to abort the takeoff it wouldn’t be able to roll to a safe stop with the required X amount of extra runway leftover.
Now, repeated across the umpteen thousand flights every year, these margins keep everyone safer. If dodgy outfits started cutting out these margins, there would certainly be more airline crashes.
Hot all the time is not a problem - the expected heat is simply factored into the situation. It’s “hotter than we expected it to be when we booked the passengers” that’s the problem.