Page 24 - March 2023

ASK THE EXPERT
Takeoff OAT Restrictions
by Tom Clements
During one of the past King Air Gatherings, I was asked about engine ice vane usage on the ground. Specifically, a concern was expressed about a temperature restriction stated in the Pilot’s Operating Handbook (POH) for the model 200-series. Is a limit being violated at times when ice vanes are being used? A follow-up question asked about a similar concern for the 300-series. I plan to review and discuss these questions and more in this article.
not the same as “ISA + 37°C.” ISA stands for “International Standard Atmosphere,” the engineering- accepted model of the average worldwide atmosphere. This is the one with a Sea Level temperature of 15°C or 59°F and a lapse rate of 2°C for each 1,000 feet up to the stratosphere that starts at FL350. ISA + 37°C is a shorthand way of saying, “The OAT that is 37°C above the standard temperature for that altitude.”
Therefore, at Sea Level, the King Air’s limiting OAT for operation
Realize that all King Airs have an OAT limit above which they are not allowed to operate. In almost all cases this is expressed as ISA
22 • KING AIR MAGAZINE
+ 37°C. Many folks think “Golly, 37°C is only 98.6°F, so there’ll be lots of times that we cannot fly!” Wrong! The 37°C temperature is
MARCH 2023