Re: Hot days and performance
We've been having some hot days in Brisbane lately with Amberley getting up to 40C. Is the performance degradation noticeable on the A380 or just another factor to be considered by the iPad?
On a flight from DCA earlier this year on a >38C our aircraft took a lower load of fuel and topped off at Nashville for extra fuel.
Is the A380 ever in this situation or only ever operates from decent sized runways.
As it gets hotter, the effect is felt as if you are already at altitude. This is called 'density altitude', and is explained here:
Density altitude - Wikipedia, the free encyclopedia
The engines normally have a temperature margin from their maximum, but as the air temperature rises, the margin is eaten up, until you reach the point that max EGT is reached before the normal max RPM limits....which means that the power available is reduced.
As the runway length, and wind conditions are fixed for any given take off, as the temperature rises it will have the effect of reducing the maximum weight available. Most iPad/OIT calculations give us performance limited numbers that are well above the max structural weight. So, in the normal course of events, with the A380, as long as we are operating into the wind, we'll be able to get to max weight. It occasionally becomes limiting though. In Melbourne last year, it was 46º on one occasion, and the wind was a crosswind that was basically at 90º to the runway, but moving around a bit. As we do our calculations on the worst case, that meant that we'd potentially end up with a slight tailwind on either 16 or 34...and according to the laptops that put our actual weight above our performance limited weight...i.e. too heavy to take off. In that case the only solution was to wait for the change to come through, which had the effect of moving the wind slightly to the south, and meant that the calculation no longer required any tailwind.
In the sim the temperature effects can become evident at other times. Practicing a two engined out approach to a really hot Dubai, you'd find that the aircraft would be unable to maintain level flight with the gear down, whereas it's normally just able to manage that...so that makes it important to ensure that you time to gear down section to just prior to intercepting the glideslope.
