Just to continue the bar room chat ….
When a pilot calculates their take-off performance figures using the Onboard Performance Tool for runway 27, they see a little note at the bottom of the page that says;
‘
This runway has 90 degree line up turn’
and some of them remember back to the last time they read their Training manual to a specific sentence that says;
Turns of 90 degrees or moreInitiate the turn as the intersecting taxiway centerline (or intended exit point) approaches approximately the center of the side window.
and then they start to shiver thinking about how grumpy ATC will get if they do that while someone is at 900ft on final, so that flick to the next page of the OPT to see how much fat they have in their figures.
If they are in a typical 24K 737 at 73 tonne, and the runway is wet with no wind, 15 degrees, 1013, they will see that it will take them 2330m to accelerate and then stop and that the ASDA is 2346m. They have 16m up their sleeves predicated on the 90 degree line up. They then start biting their finger nails as they balance the very low probability of having to reject at V1 against the orderly flow of traffic and attracting the ire of the controller and a weary eye roll from their f/o. It’s about this time that they remember the sentence from the Operations Manual that states;
Flight test and analysis prove that the change in takeoff roll
distance due to the rolling takeoff procedure is negligible when compared to a
standing takeoff.
and wonder if that sentence is comparing a standing start with brakes applied v’s a rolling start from the same position, or if it’s comparing a 90degree line up with more relaxed rolling line up? The subject has never been discussed with them in all their years of flying training and they simply aren’t sure, so they take the conservative route, and the ire, and the eye rolls, and do the best they can on the day to meet their responsibilities.
Does any of that sound plausible or familiar to you guys? I think it’s the kind of balancing act that goes on and with a broad spectrum of personality types in the industry you will always get folks that are more conservative and process driven than the average. We can see it with individual controllers sometimes as well.