Well if ground idle is set at 61 N1 or Ng then in very cold temps the T5 is going to be low. Perhaps P+W are worried that the temp could be low enough to cause a flameout followed. by a big “WHOMP ” and T5 spike if it relights. Just a thought.
What engine and what is the min T5 idle limit?
Joke)As a bit of thread drift I talked to a Puma pilot who when slinging a load in very heavy rain had the temp of both engines just hovering at the very bottom of the green arc It got their attention as it occasionally dipped below the green. They were slinging drill pipe so were pulling a lot of power. Nothing happened, no surging or Torque fluctuations. Strange way to do a compressor wash. ) Joke Over