How can an airplane's fuel be "too hot"?

Factual Questions
21

Not to mention the balance of fuel that goes into the wings of such aircraft. I used to fuel Brasilias and other smaller aircraft whan I worked as an airplane refueler at Dulles airport in the DC area for Ogden Allied Aviation Services. The pilot would send a directive for fuel to us, and we would pump exactly the same amount into each wing. On the real small planes, you could actually see the plane tilt a little after you put 160 pounds of fuel into one wing before you fueled the other and it righted itself.

I once fueled the Concorde (British Airways). That fucking thing took 160,000 lbs of fuel…per wing! And according to the British Airways ground crew, used almost a third of that just taking off and getting to supersonic cruising speed!

It took almost two hours to fuel that thing with two pumper trucks parked under each wing.

I have to say that those Brits were really cool. They let me go up into the cockpit and sit in the pilot’s seat of the Concorde. What a treat! I felt like Luke Skywalker getting ready to battle the Deathstar. So many switches, readouts, gauges, controls…it was unbelievable.

22

And its just NOT heat.

Its heat AND humidity (and altitude of course).

The higher you are, the less dense the air is and the “harder” it is to fly.

The hotter the air is, the less dense it is and…

But hot AND humid air is EVEN less dense than just humid air or hot air. Fortunately, when its usually BOTH hot and humid, its very low altitude. But not always.

23

Ahah! Found the article I was looking for.

Salon.com runs a column by a veteran airline pilot, titled (appropriately) Ask the Pilot. This column, in particular, addresses the issue of canceling a flight due to the heat. I think he’s saying the same things that everyone else has mentioned so far, but it deserves a quote for being concise and from someone who really knows what they’re talking about.

24

There are two different issues here. The OP is asking about fuel which is too hot. Many other posts are addressing hot weather.

Hot weather increases the amount of runway required for a given aircraft at a given weight. There can come a point when the runway is not long enough to allow a successful takeoff, and that is when either passengers, luggage or cargo are offloaded.

If the fuel is too hot the flight isn’t going, no matter what the load. Unfortunately I don’t know exactly what the ramifications of hot fuel are, but as BlakeTyner points out, there is a particularly well known and tragic example of what can happen due to hot fuel vapor.

25

Pssst. See post 4.

26

While courting Mrs. Plant and flying to Boston from Little Rock, I was leaving the hub for LR National in a little two engine prop aircraft with, apparently, Youth Overeaters Anonymous. The co pilot rearranged the sitting, claiming that the baggage had been stowed badly. You could see the aircraft leaning to one side. :slight_smile:

27

I fly Dash 8s, I’ll try and look up the manual for some specific information (although the manual tends not to tell you anything more than you “need to know”.) In the meantime I leave you with this.

I think you’re daughter probably suffered an unnecessary delay. There are fuel temperature gauges in the cockpit, I can’t remember the limiting temps off the top of my head, but there is a large green operating arc that the needle normally sits in. The temperature probes are situated such that they sometimes show an excessively high temperature on the ground shortly after the engines have been shut down. This can mean that the temp is high when it’s time for the next flight if the turn around time is short.

In my experience, if you just start the engines anyway, the temperature comes down within seconds and you’re good to go.

The issue with fuel temperature is more to do with it being too cold. If it is very cold, it can freeze and that may cause the engines to flame out. Having the fuel too hot doesn’t seem to be a big issue. If the fuel is hot in flight, the manual just directs you to turn on the fuel boost pumps and monitor the temperature, it doesn’t say you have to land immediately or anything like that.

There’s no need to get actual weights from passengers as long as the load is fairly normal. Every now and then the standard passenger weights are updated to reflect the spare tyres everyone carries with them these days. The current standard weights in Australia are 190 lbs for men and 156 lbs for women. Having said all that, there is a key part of the regs which state that if the load is abnormal, all passengers must be weighed. So if your passenger list is made up of particularly heavy people, e.g., you’re taking a couple of football teams somewhere, then you must weigh everyone.

Ultimately, if your aircraft is a bit heavier than expected, it doesn’t matter, there is enough fat built into the performance calculations to account for inaccuracies in the system.

Although humidity does effect density, I can only assume that it is a small effect compared to temperature, as our own take-off performance charts do not account for varying humidity, only temperature, altitude, and wind.

28

Whoops. I guess that’s why that particular excerpt was rattling around the back of my head…

29

Righto, some further information.

There is a fuel tank temperature gauge which has no published limitations. The fuel itself is supplied to the engine driven fuel pump via a fuel filter and heater. The fuel is heated by engine oil. As I said in the previous post, it is generally cold fuel which is the danger, hence it is heated. The fuel temperature is sensed after it has been heated and prior to entering the engine driven fuel pump.

Because the temperature sensor is in the engine nacelle, it can read an abnormally high temperature after the engine is shut down, as the engine is still hot but there is no longer cold fuel flowing through the system.

The limitations are 11C to 57C and the manual prohibits continuous operation with the fuel above 57C. So in the situation your daughter was in, we’d have noted the high temperature, conducted an engine start and checked that the fuel temperature dropped immediately.

On further reflection, I’d say that humidity is always assumed to be 100% in take-off performance calculations as the assumption is that you will be taking off in cloud.

30

[quote=“1920s Style “Death Ray”, post:27, topic:497061”]

Although humidity does effect density, I can only assume that it is a small effect compared to temperature, as our own take-off performance charts do not account for varying humidity, only temperature, altitude, and wind.
[/QUOTE]

It is definitely less significant than temperature, but a bit more than trivial. Googling produces plenty of sites with density altitude calculators (such as this one) that you can play with to see the effect of temperature and dewpoint changes.

31

Yeah, as I said above, I think they just assume 100% humidity. The performance charts are valid for all weather conditions.

I had a look at the specs for Jet A1 and couldn’t find anything significant about 57C. I suspect it has more to do with the operating temperature of the fuel pumps than anything else.

32

[quote=“1920s Style “Death Ray”, post:27, topic:497061”]

I fly Dash 8s, I’ll try and look up the manual for some specific information (although the manual tends not to tell you anything more than you “need to know”.) In the meantime I leave you with this.

I think you’re daughter probably suffered an unnecessary delay. There are fuel temperature gauges in the cockpit, I can’t remember the limiting temps off the top of my head, but there is a large green operating arc that the needle normally sits in. The temperature probes are situated such that they sometimes show an excessively high temperature on the ground shortly after the engines have been shut down. This can mean that the temp is high when it’s time for the next flight if the turn around time is short.

In my experience, if you just start the engines anyway, the temperature comes down within seconds and you’re good to go.

The issue with fuel temperature is more to do with it being too cold. If it is very cold, it can freeze and that may cause the engines to flame out. Having the fuel too hot doesn’t seem to be a big issue. If the fuel is hot in flight, the manual just directs you to turn on the fuel boost pumps and monitor the temperature, it doesn’t say you have to land immediately or anything like that.

There’s no need to get actual weights from passengers as long as the load is fairly normal. Every now and then the standard passenger weights are updated to reflect the spare tyres everyone carries with them these days. The current standard weights in Australia are 190 lbs for men and 156 lbs for women. Having said all that, there is a key part of the regs which state that if the load is abnormal, all passengers must be weighed. So if your passenger list is made up of particularly heavy people, e.g., you’re taking a couple of football teams somewhere, then you must weigh everyone.

Ultimately, if your aircraft is a bit heavier than expected, it doesn’t matter, there is enough fat built into the performance calculations to account for inaccuracies in the system.

Although humidity does effect density, I can only assume that it is a small effect compared to temperature, as our own take-off performance charts do not account for varying humidity, only temperature, altitude, and wind.
[/QUOTE]

Thanks for the clarifying information. So many folks seized on hot weather and its effect on air density. That wasn’t so much the issue in this case. The temp in Colorado Springs was about 20C at an altitude of 1886 meters. It was not an unusually hot day.

The Dash-8 in question makes round trips between DEN and COS (about a twenty minute flight). It had just rolled up to the stand, shut down the engines, off-loaded its passengers, and loaded the new passengers. Since it is a short turnaround, how does a Dash-8 crew avoid delaying every flight due to “hot fuel”? Had the crew simply started the engines, they may have gotten the temp they wanted? My daughter said something along the lines that the crew said they were trying to cool the fuel, but it wasn’t working.

The Dash-8 has been in the news lately here in the USA. A Dash-8 crashed in New York state a few months ago and the authorities are now saying that pilot and co-pilot fatigue and inexperience were significant factors in the crash. Like the New York Dash-8, my daughter’s flight carried the livery of a large airline but was actually operated by a small carrier. However, it is springtime here in USA and the New York crash happened in the dead of winter in a cold part of the country. (Wing icing seems to have been the main culprit, but the crew may have been able to handle it better had they been thinking more clearly.)

33

Was this a Dash 8 400 or an earlier model? I fly 200 and 300 series Dash 8s. The 400 has a lot in common with the smaller ones, but it does have some significant differences. If it was a 400, my information may not be relevant.

I don’t know how they deal with it. In our company we do 6 to 7 hour flights and each aeroplane normally just flies once per day. I have not seen anything in the manual that dictates what to do if the fuel temps are high. I know of the problem because my very first flight in a Dash 8, the aircraft had just flown and the (new) captain noticed the fuel temps were high. The engineers were called over and they told us to start it regardless and the temps would drop. So that’s what we did. I’ve seen it again in similar circumstances and have treated it the same way. It doesn’t always happen when there’s a short turn around. Although it is rare for me to do a short turn around, I do them occasionally, and normally the fuel temps stay in the green arc.

The latest I’ve seen on the Colgan Dash 8 crash in New York was that it was entirely crew error. The ice had no impact except that the anti-ice system was turned on and this increases the speed at which the stall warning devices activate. This means that the crew were probably surprised when they activated at a faster airspeed than normal. After that the crew reacted poorly and turned an embarrassing situation into a fatal one. The reaction of the crew is a product of training, experience, expectations, etc. There’s been some speculation that the manner in which stall training is conducted in the US actually forms incorrect muscle memory which may cause a pilot to react the wrong way to a stall warning.

The issue of small aircraft carrying the livery of larger airlines is common around the world. It is in the airline’s long term interests to make sure that the operating company has a high standard, but sometimes they get caught out.

34

^^ I spent a little while googling hot fuel temps and after about ten pages worth of nothing except freezing warnings, gave up. I can’t imagine any kind new procedure regarding fuel temps coming down as a result of that crash, and since you’re pretty much confirming there’s no aircraft problem with hot fuel temps, I can only guess that it was an excuse for something else that was more embarrassing to the airline, like a late/sick pilot, maybe the fuel truck unexpectedly ran out or broke–who knows.

35

Both the Colgan Dash 8 and the one my daughter was aboard in Colorado were 400 models. I must have misremembered the details of the investigation. I remember that ice was initially suspected, but that the crew’s reactions to the crisis were less than adequate.

1920s Style “Death Ray”, thanks for taking time out of your schedule to post your experiences. Six or seven hours on a Dash 8 seems like a really LOOOOONG time on such a small plane. Safe journeys.

36

I’m always happy to talk about aviation, and my schedule is pretty relaxed, I fly about 10 days a month. The flights don’t seem so long. We do ocean patrols for Australian Customs so we’re normally busy investigating boats or if it’s quiet, we talk about shit. The Dash 8 is not bad to spend that sort of time in, it’s big enough to be able to stand up straight and it’s got a toilet, galley, microwave, etc.

I think you’re remembering the Colgan accident correctly. They initially suspected ice, but further investigation has shown that ice wasn’t a direct factor. The full story won’t be public until the final report is released I guess.

37

[quote=“1920s Style “Death Ray”, post:36, topic:497061”]

I’m always happy to talk about aviation, and my schedule is pretty relaxed, I fly about 10 days a month. The flights don’t seem so long. We do ocean patrols for Australian Customs so we’re normally busy investigating boats or if it’s quiet, we talk about shit. The Dash 8 is not bad to spend that sort of time in, it’s big enough to be able to stand up straight and it’s got a toilet, galley, microwave, etc.

I think you’re remembering the Colgan accident correctly. They initially suspected ice, but further investigation has shown that ice wasn’t a direct factor. The full story won’t be public until the final report is released I guess.
[/QUOTE]

I assumed you were in passenger service, so when you said you had six or seven hour flights, I was thinking that was an awfully long time to sit shoulder-to-shoulder with a bunch of people. For just an air crew, though, I’m sure it’s great. I also wondered why an airline would want a seven hour flight in a Dash 8 when a jet would seem to be much more efficient for such a long trip. The Dash 8 isn’t even pressurized.

Well, it seems to me that the “hot fuel” reported was bullshit for some other flight delay, or perhaps over-caution on the part of an inexperienced flight crew. It ended up delaying my daughter by twenty hours by the time she could get booked onto an available flight home. It cost her a day’s work. Hot fuel my ass.

38

The Dash 8 is pressurised. Max flight altitude is 25000 feet and the cabin is typically pressurised to 8000 feet. Except for the transit legs to our search area which are flown at max altitude, we normally operate between 200 and 1500 feet. A jet would be nice, but they aren’t very economic for our job.

39

I guess our flight from DEN to COS was just too short. The flight attendant said that we would not exceed 10000 feet and that the cabin would not be pressurized. There was no discussion of how to use the air-masks during the pre-flight safety lecture and there did not appear to be doors for the masks in the overhead consoles. Maybe they were there, but I didn’t see them. (I’ve flown the same flight that my daughter was on.) I can see how a jet wouldn’t be good for low-speed, low-altitude inspection of marine traffic.

40

It doesn’t have drop down masks. It doesn’t fly above 25,000 and can descend from that altitude to 10,000 feet within 4 minutes which means it doesn’t require drop down masks.

DEN to COS is short enough that 10,000 is a reasonable cruise altitude, but it is unusual that it wasn’t pressurised. In normal operations the pressurisation is always working regardless of how high you go (for example, when we’re flying it at 1500’, the cabin altitude is maintained at sea level.) It might have been unserviceable.