High and hot

There are several factors at play with high and hot conditions. We all learn as students that such conditions can dramatically increase our takeoff distance. In fact, in some cases it can lead to a takeoff roll and climb over a tree that exceeds the length of the available runway. In jet aircraft, the issues begin with the impact of single-engine climb performance, because our takeoff performance is predicated on being able to climb out after an engine fails.

Some airports have challenging terrain that requires complex single-engine climb procedures to ensure terrain clearance. These procedures are almost always airline and fleet specific.

Another issue is tire speed. Every tire has a maximum groundspeed. Hot days can have you toeing the edge of that limitation, and the takeoff may not be possible, even if the airplane can theoretically make the takeoff. It’s rare, but it happens. In fact, in Denver in the summer, I routinely see groundspeeds that can be uncomfortably high.

Speaking of tire speeds, the groundspeeds can come into play with a high-speed rejected takeoff (RTO), because the brakes will be pushed to the limits as well. Airline brakes have a pin as part of the brake assembly that will deflate the tire if brake temperature gets too high. This is done to avoid a brake fire. In the event of an RTO on a high and hot day, brake cooling charts must be consulted, and if the conditions warrant, another takeoff may not be possible for well over an hour.

A final item that needs to watched is the EGT. I recently had an airplane that was running high on the EGTs on one of the engines, and more than one crew had written it up for being higher than normal. It was clear that the engine was going to be removed soon, but as long as the mechanics could verify that it was operating within limits, they had no choice but to put it back in service. It didn’t matter if it was within 1 degree of the limit of 101 degrees—in limits is in limits. That being said, the EGTs were front and center for attention, especially on the takeoff.

There is one area that an airline has some control over with respect to performance. Performance data is sold by various vendors, be it the manufacturer or a third-party company that specializes in producing data that is safe and cost-effective. Most of the time, the high end of the temperature range stops in the low 100s (Fahrenheit). However, for a not-so-small fee, the carrier can purchase performance charts and data for much higher temps, such as those found in the desert southwest or the Middle East. If there is reason to believe that such extreme measures will be needed enough, it’s a price worth paying. Otherwise, flights can get canceled on the rare days that temperatures exceed the limits of the book (and budgets).