Ignition.
Escape Path, remember that when a turbine engine is started the ignition is turned off. The flame continues to burn on it's own provided it is not disturbed. It doesn't cost anything to turn the ignition on, so for peace of mind, use it. It's a lot more of a problem trying to do an "air start" than to put the switch to on.
On most big jets you have to be below 28,000 ft and above 280 Kts to get a relight. Hope this helps.