Should you line-up the runway 90 degrees or follow the yellow marking?

Question

I had a discussion with somebody recently. I prefer to do a 90 degree line-up on the runway, ensuring max take-off run available. (in GA airplanes...) However, somebody pointed out that one should follow the yellow line, which I disagree with. Aren´t they only to vacate the runway? Are there any official guidelines or truth to this? Thanks in advance!

Answer 1

Here's a commercial aviation response, but almost certainly applicable to general aviation, too.

Take-off distances are commonly measured from the threshold or, for intersections, the downwind edge of the taxiway (note that might actually depend on local regulations - might be worth checking the AIP). In any case, to achieve certified take-off performance, you need to replicate the geometric relation between main gear and runway threshold as closely as possible, which in essence most probably means a minimum distance line-up most of the time.

If you operate on runways much longer than your performance limitations, it doesn't really matter in practice, but that doesn't change the theory.

See e.g. the referenced document from Airbus publishing takeoff performance corrections for non-standard line-ups, and the baseline is a 90⁰ entry with minimum distance, ignoring any nicely curved yellow lines:

Airbus document

Having said all that, this is the performance engineer's view. I am not certain as to whether there's anything anywhere in the regs (however, if there was, it would have been commonly ignored and actively trained against in all airlines I used to work for).

Answer 2

Places I used to operate from were generally quite busy (GA and otherwise). That necessitated taking into account the often long queue of planes behind you, so the lineup was done in about 60 degrees to avoid blasting planes behind you with propwash when doing the run-up. On the rare occasions one was the only plane taking off, and in places where run-up at RWY lineup was not allowed, I was taught to obey the lines. "They don't paint them on the tarmac just for sh_ts and giggles."