Is the limit on start up temperature or operating ?. Surely once you have started the OAT is not really relevant for the engine and gearboxes . Might have more effect on rotor hub seals and elastomers . If I recall correctly the BK117 had special seals for Low temp ops that were no good at higher temps. We also had to change all the boots as the naugahyde would get brittle at low temps there was a booster fan in the heating ducts as well I think.