B777 OPT questions
Using VHHH / Hong Kong as an example, let's say the ATIS gives the following :
departures 25L
29 degrees Celsius temperature
1006 hectopascals QNH
3 knot headwind component
I use 30 degrees C, 1005 hP, and a 5 knot tailwind component in the OPT.
In other words, I plan for a slightly worse case scenario. I'm covered if any of those parameters change resulting in better takeoff performance, that is temperature goes down or QNH goes up or wind really does give a headwind component.
1.
Any reason to not continue this practice ?
2.
Haven't been able to find a reference as to when new numbers MUST be calculated with the exception if actual weight is higher than planned weight. In this example, at what temperature is recalculating a must do - 31 degrees ? 32 degrees ? How about QNH - if it goes down to 1004 hP ? 1003 hP ?
It's my understanding that the OPT has some built in buffers and calculates take off numbers in a very conservative way. I want to avoid having to recalculate numbers if ATIS or actual parameters change not in favour of better takeoff performance at a inconvenient time. In the queue for takeoff, for example.
Thanks all.