Hi JB,
I'm going to LAX on QF93 this morning. Is a temperature of 44 celsius and wind of 15 knots affecting take off performance so much so that they would need to remove some freight or pax compared to a 25 celsius day? Or is the runway long enough in MEL that this is never a problem with the LAX flight?
As long as the wind is a headwind, then there are hardly ever any issues. The big problem comes up when the wind is a crosswind, but flicking around a bit in direction. Then we have to allow for the worse case, which may well be a tail wind. Combine tail wind, high temperatures and heavy weight, and you can conceivably reach a point at which you can't take off. In the current Melbourne heat wave, the issues are more likely to affect the Dubai flights than those to LA. Although the flight times are similar, the LA flight is going with the wind, and is generally about 20 tonnes lighter.
We hit the problem the other day. With the worst case wind, the performance limited take off weight was less than the weight we wanted. The first options you have are to change the take off parameters away from what we normally use. For the sake of standardisation, we normally use Flap 2 for take off, and the packs are fed their air from the engines. Flaps 1(+F) and Flap 3 are also available, and can often give quite a gain. Packs can be turned off entirely (not a top idea when it's over 40º) or run from the APU until after take off. The combination of the two might get you another 15 tonnes depending upon the actual conditions.
As a passenger is only about 100 kgs or so, it becomes a bit pointless if I need multiple tonnes. Much the same applies to cargo.
The next option that can be looked at if there is no other way of either improving the performance limit, or reaching it, is to dramatically reduce the fuel load, and to make a tech call. That option was looked at the other day, and would have been quite viable given the the route for the day was closer to Perth than normal. A preplanned splash and dash can be done in about 30 minutes.
The option we actually employed was to have a chat to our met people, who were adamant that a slight southerly change was overdue. That was expected to swing the wind enough that we'd get rid of the tail wind problem....and with a slight delay to our departure, that's exactly what happened.
Even my car didn't like the heat the other day. After enduring up to 45º on the drive, it gave me an engine management fault just approaching the car park. Fingers crossed that it's reset itself in the intervening week, otherwise I expect it will be off on a truck to a dealer when I get back...so no quick drive home I guess.
