Hot heavy departure
Discussion
Couple of questions. Last night I was coming home from Corfu, and our flight was delayed in boarding. Once on the aircraft the captain (very professionally) stood upfront and addressed the cabin, explaining we had a bit of an issue.
Due to the high ambient temperature (30c) and the short runway at Corfu, we were unable to load the required amount of fuel for our destination of Glasgow, and would be flying up the Italian coast and fuelling in Venice.
No problems at all, if a bit hot n sweaty during the uplift of fuel as no available AC (no engines and I'd imagine no APU)
My concern was, during the take off run, if we had a problem close to V1 or an engine failure around or after V1, just how uncomfortable for the flight crew would this have been. There is some high ground on the runway heading, and the runway end is so close to a road that they stop the traffic for departures.
Also, 30c isn't unusual in Greece. Just how oftern are takeoffs limited by this sort of thing.
Thanks
Due to the high ambient temperature (30c) and the short runway at Corfu, we were unable to load the required amount of fuel for our destination of Glasgow, and would be flying up the Italian coast and fuelling in Venice.
No problems at all, if a bit hot n sweaty during the uplift of fuel as no available AC (no engines and I'd imagine no APU)
My concern was, during the take off run, if we had a problem close to V1 or an engine failure around or after V1, just how uncomfortable for the flight crew would this have been. There is some high ground on the runway heading, and the runway end is so close to a road that they stop the traffic for departures.
Also, 30c isn't unusual in Greece. Just how oftern are takeoffs limited by this sort of thing.
Thanks
No mention of humidity or pressure during the wee chat the captain gave, and I think some of the other stuff posted looks about right.
I'm certain no risks were taken, the impression was that anything would be done to avoid em. I just started wondering during the takeoff roll (which was revvy) that any extra issue would've made things awkward. Thankfully no probs.
I'm certain no risks were taken, the impression was that anything would be done to avoid em. I just started wondering during the takeoff roll (which was revvy) that any extra issue would've made things awkward. Thankfully no probs.
Simplistically.
Airliners operate to something termed 'Scheduled Performance Class A'. What this means is that, as long as the T/O calculations have been done correctly in cases of loss of the most critical power unit before V1 (stop-go decision speed), then the a/c will stop in the R/W remaining; loss of said power unit after stop-go decision speed and the a/c will get airborne and climb to engine out stabilising height.
Essentially there are 3 parameters that affect this calculation. These are Field Length, Aircraft weight, and Engine performance.
Field length comprises:
TORA - Take Off Run Available. This is effectively the available ground roll.
TODA - Take Off Distance Available. This is the ground roll plus an area clear of obstacles for the initial climb out.
ASDA - Accelerate/Stop Distance available. This is basically the TORA plus any extra stopping area.
Aircraft weight is a function of APS weight (Aircraft Prepared for Service) ie how much the airframe weighs, Zero Fuel Weight (ZFW = APS weight + cargo/pax weight) and Aircraft Operating Weight (ZFW + Fuel weight).
Engine performance is a function of Density Altitude - ie how hot and thin the air is.
The upshot of all this is that, for a given R/W, in given conditions, there will be a Maximum Regulated Take Off Weight (MTOW). Now, obviously the MTOW will be made up of ZFW and Fuel Weight.
As temperature rises, and/or as altitude rises then the engine performance will be less. The aircraft will not accelerate as well so the GO speed will get closer to the far end of the R/W. Associated with this (and owing to brake energy), the STOP speed will get closer to the threshold. In order to balance this out MTOW has to reduce. If MTOW reduces for a given ZFW then the Fuel Weight must reduce. If the Fuel Weight reduces then the range of the a/c (and its Diversion performance must also reduce.
Airliners operate to something termed 'Scheduled Performance Class A'. What this means is that, as long as the T/O calculations have been done correctly in cases of loss of the most critical power unit before V1 (stop-go decision speed), then the a/c will stop in the R/W remaining; loss of said power unit after stop-go decision speed and the a/c will get airborne and climb to engine out stabilising height.
Essentially there are 3 parameters that affect this calculation. These are Field Length, Aircraft weight, and Engine performance.
Field length comprises:
TORA - Take Off Run Available. This is effectively the available ground roll.
TODA - Take Off Distance Available. This is the ground roll plus an area clear of obstacles for the initial climb out.
ASDA - Accelerate/Stop Distance available. This is basically the TORA plus any extra stopping area.
Aircraft weight is a function of APS weight (Aircraft Prepared for Service) ie how much the airframe weighs, Zero Fuel Weight (ZFW = APS weight + cargo/pax weight) and Aircraft Operating Weight (ZFW + Fuel weight).
Engine performance is a function of Density Altitude - ie how hot and thin the air is.
The upshot of all this is that, for a given R/W, in given conditions, there will be a Maximum Regulated Take Off Weight (MTOW). Now, obviously the MTOW will be made up of ZFW and Fuel Weight.
As temperature rises, and/or as altitude rises then the engine performance will be less. The aircraft will not accelerate as well so the GO speed will get closer to the far end of the R/W. Associated with this (and owing to brake energy), the STOP speed will get closer to the threshold. In order to balance this out MTOW has to reduce. If MTOW reduces for a given ZFW then the Fuel Weight must reduce. If the Fuel Weight reduces then the range of the a/c (and its Diversion performance must also reduce.
Edited by Ginetta G15 Girl on Tuesday 1st September 23:04
Glosphil said:
Ginetta G15 Girl said:
What the f does that have to do with anything?
Perhaps if you asked him nicely with less implied bad language he might enlighten you to the reason for his comment.fridgedoctor said:
Couple of questions. Last night I was coming home from Corfu, and our flight was delayed in boarding. Once on the aircraft the captain (very professionally) stood upfront and addressed the cabin, explaining we had a bit of an issue.
Due to the high ambient temperature (30c) and the short runway at Corfu, we were unable to load the required amount of fuel for our destination of Glasgow, and would be flying up the Italian coast and fuelling in Venice.
No problems at all, if a bit hot n sweaty during the uplift of fuel as no available AC (no engines and I'd imagine no APU)
My concern was, during the take off run, if we had a problem close to V1 or an engine failure around or after V1, just how uncomfortable for the flight crew would this have been. There is some high ground on the runway heading, and the runway end is so close to a road that they stop the traffic for departures.
Also, 30c isn't unusual in Greece. Just how oftern are takeoffs limited by this sort of thing.
Thanks
Ginetta G15 Girl is absolutely correct with her Perf A description, and having looked at the documentation for Corfu airport I add the following:Due to the high ambient temperature (30c) and the short runway at Corfu, we were unable to load the required amount of fuel for our destination of Glasgow, and would be flying up the Italian coast and fuelling in Venice.
No problems at all, if a bit hot n sweaty during the uplift of fuel as no available AC (no engines and I'd imagine no APU)
My concern was, during the take off run, if we had a problem close to V1 or an engine failure around or after V1, just how uncomfortable for the flight crew would this have been. There is some high ground on the runway heading, and the runway end is so close to a road that they stop the traffic for departures.
Also, 30c isn't unusual in Greece. Just how oftern are takeoffs limited by this sort of thing.
Thanks
Whilst the airport is (obviously) at sea level, the runway is 7700' long. This isn't particularly big by modern standards, but is what I'd term a 'medium' length runway for an international airport and more than suitable for what is probably an A320/737.
The kicker is that there is an obstruction near the end of the runway that requires an unusually steep climb to surmount. So this means that given the right combination of variables, including aircraft weight, field length, altitude and temperature, wind direction and strength, and subsequent engine performance: having done all the maths the sensible option to make sure that you can achieve the climb gradient is to not take fuel for the full journey and to make sure you can get over the obstacle with all your fare-paying passengers on board.
Hope that lightens the mood slightly and any concerns you may have about safety during international air travel
EDIT: Seen you've posted the question on PPRuNe and got a similar answer
Edited by rkem on Wednesday 2nd September 02:13
Ginetta G15 Girl said:
BOH said:
Let me guess, this was an Airbus, right?
What the f does that have to do with anything?In answer to the OP's question, the reality is that this happens a lot more than we'd like.
From an operational point of view, a tech stop for fuel is a pain in the proverbial wasting a lot of time and money. We want to avoid them at all costs if we can.
Often there's not a lot in it and a few hundred kilos would make the difference, but the rules are that if the figures say no, then you either have to offload passengers and/or bags to reduce weight or put on the fuel you can and go somewhere with a longer runway to top up the tanks. The second option is very much preferable compared to dumping passengers!
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