Hot and Bothered

Hot and Bothered

Summertime pre-flights can be a pain. By the time I am finished with all my chores on a 100-degree ramp, I am uncomfortably drenched in sweat. I tend to rush things hoping to get in the air sooner and to cooler temperatures. By contrast, a preflight on any summer morning in Gunnison, Colorado is delightful. I am relaxed in the cool mountain air. My attitude is great and my performance is better.

Interestingly, heat effects my Mustang’s performance the same way.

Temperature affects all engines, but jet engines even more so. The Pratt & Whitney PW615F’s on the Mustang perform well at standard temperatures (ISA), but start adding some heat and the “little engines that could” can’t. My unscientific data indicates that ISA+ temperatures are more prevalent in the lower flight levels especially on the Addison (KADS) to Gunnison (KGUC) trip I make often. I usually see ISA+5 at FL390 decreasing to ISA+0 at FL410. The Mustang performs better (fuel flow versus true airspeed) at FL410, but you have to get there to take advantage of the performance. And getting there is the challenge.

Take Tropical Storm Cindy, for example.

Tropical storms dramatically disturb normal weather patterns with low level, very warm moisture. Our June near gross weight morning departure from Dallas to Pellston, Michigan (KPLN) was going to be a breeze. Our flight plan placed us just west of Cindy’s track and projected an initial tailwind of 18 knots increasing to more than 95 knots near the destination. It sounded simple on paper. But in order to get to FL410 you have to climb past all those other flight levels and Cindy was wreaking havoc with the temperatures.

I first realized the situation when I looked at the temperature reading on the G1000 PFD and saw ISA+17 at 10,000 feet. Out of FL240 it was ISA+15 and the Mustang was huffing and puffing. Center was accommodating with our very slow climb because even the airlines were complaining. Finally, after an eternity we leveled at FL410 in ISA+0 temps and rode the wind to Pellston. Two days later, I was more prepared and studied the temps at ALL altitudes, realizing that although a nonstop home was possible, climbing to FL400 in the hot temps would simply not work.

A fuel stop in St. Louis (KSUS) was the prudent decision.

Takeoffs from Gunnison, at 7,680 MSL, require some planning, too. For a summertime nonstop to Dallas, my personal surface temperature limits are 10 degrees Celsius. This normally allows for a 3.3 degree climb after an engine failure. And although this climb performance is not technically required in the normally clear skies of Gunnison, an actual engine failure in any conditions is an eye-opening, seat-staining event. Try it sometime with a qualified mentor or instructor. It’s amazing how big those pretty mountains are.

It’s nice to know what kind of performance is available. If you haven’t done so, run some performance numbers on your airplane at hot/high airports. There are many scenarios where you will have little to no climb performance in case of engine failure. Resist the temptation to depart just because you see others doing so.

In icing conditions, temperature also dramatically effects climb performance in the CJ, CJ1, CJ1+ and M2 Citations. Those airplanes have wing heat derived from diverted engine bleed air. The worst situation is a climb in icing conditions at high ISA+ temperatures. The Williams engines simply don’t produce enough extra thrust to warm the wings and climb the airframe very quickly.

Cessna says they have a solution for this dilemma: It’s a multi-million-dollar service bulletin they call the CJ3+. For you Embraer fans, the part number is P300.

But all this talk of spending money has me hot and bothered. I need a shower.

Fly safe.

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