Photos by Clint Goff
I’ll never forget flying Saab 340s with American Eagle Airlines many years ago. I flew as a first officer and sweated more than the law should have allowed, not from unrelenting stressful situations but because the Saab 340B was not designed for hot weather. The aircraft is designed and built in Sweden, and Swedish aircraft designers must know little about Texas heat. I remember being in long lines of airliners awaiting takeoff clearance at Dallas Fort Worth International Airport, the right engine feathered and the environmental switches set for full cold, yet the wimpy airflow from the gaspers was just not enough. We had a full load of passengers with everyone sweating bullets, complaining and occasionally getting sick.
There was nothing that could be done. The Saab 340 environmental system did not have the capability to keep up on even a mildly warm day. On a really hot day, the airplane was dangerously hot. The unofficial slogan of American Eagle was “American Eagle Airlines: Where we’re not happy ’til you’re not happy.” When it came to keeping passengers cool, American Eagle had no answers with the Saab 340.
With the events of Sept. 11, 2001, when I was at American Eagle with my paltry copilot yearly income of $17,000, I knew my airline career was over. I moved out of the Saab into contract flying in the Beechcraft King Air 200 and never looked back. It was one of the best career moves I made.
The task of defeating the Texas heat did not end with my move to the King Air though. The King Air environmental system is also less than optimal, and a rookie (or untrained or uncaring) pilot can create a situation akin to a Saab 340 sweatbox too. If you have a hot day and you have a King Air flight, how do you beat the heat?
With any model King Air, you must first defeat the blazing sun. Judicious use of shade is critical. If the airplane is already in a hangar, we try to leave the airplane in the hangar for loading cargo and then pull the airplane outside just prior to passenger boarding. If at one of those nice FBOs with a big awning, palming a Thomas Jefferson to the line personnel might secure you a spot under the awning for your departure, and it’ll be worth much more than $20 if you get such prime parking.
If the airplane is in the sun, cockpit shades are critical. I recommend you only use white shades that fit the windows perfectly. Aluminum foil shades are a bad idea: The UV waves pass through the windscreen and then are reflected through the windscreen again by the highly reflective wind shades, giving them a double whammy of damaging UV sunlight. An even better option is to purchase a full cockpit cover from Bruce’s Covers (aircraftcovers.com) that guards the cockpit from the outside, truly protecting your sensitive windshield.
The window shades should also be drawn in the back of the airplane. If you have the polarizers, make sure they are still effective at doing their job.
I’ve discovered that opening the two D-windows in the cockpit and leaving the cabin door open allows for the most airflow. If there’s any wind, this trick paired with preventing incoming sunrays will stop the greenhouse effect and make your airplane far cooler for boarding.
Is ground air conditioning available?
If you live in a hot part of the world, you should own a ground air conditioner. We have one, and it is nothing more than a household window unit mounted on a rolling cart with a long ducting system. We roll the unit up to the airplane and flop the 20 feet of ducting as far into the cabin as possible. Another good option is to push the ducting through one of the D-windows in the front, which makes the cockpit coolest and the airflow migrates to the back of the cabin because the cabin door is left partially open.
Some of my favorite King Air models are those with the air conditioner compressor in the nose compartment (90 and 100 models). This allows for operating the A/C without the engine running. I cannot emphasize how good this system works. Make sure you have a really good non-battery-powered ground power unit plugged into the external power port. Then operate the environmental control system of the airplane. You can close all the doors and windows and have a completely cool cabin when you board your airplane.
However, I have a warning for you, learned from personal experience. If you plug in a battery-powered GPU (such as is found on many of the tugs with batteries), the system will draw energy from the batteries – a lot of energy. When the GPU batteries are depleted, the system will then draw down the aircraft ship batteries. I once had a mission where I thought I’d be creative and cool down the cabin, and the battery GPU was drawn down followed by the ship batteries. I opened the door to a cool cabin, but then I could not start the engines.
Worse, your ship batteries must have minimal voltage (usually 20V) to allow GPU power to operate. When I found another GPU, the power from that GPU was not available to me because the ship batteries were below 20V. I had no choice but to delay the mission by hours as I had the ship batteries removed and bench charged. I was totally embarrassed. My clients were forgiving, but I learned that systems knowledge is critically important and this is one of those things that rarely gets discussed in initial training events.
Nonetheless, if you have a good non-battery-powered GPU and a King Air model with a nose-mounted compressor, you have a unique ability that you should learn to use. Your passengers will be so impressed if you pull off that trick on a hot summer day.
For those 2XX and 3XX owners who want the ability to ground cool your airplane, Textron Aviation has a ground cooling system available (upgrades.txtav.com/products/king-air-ground-cooling). I’ve yet to see this system operational in the field, but this adds the ground cooling ability that is available in the 90 and 100 series of airplanes.
Engine-mounted compressors
If you have a King Air model with an engine-mounted compressor (2XX, 3XX), it’ll be found on the right engine and you must start that engine before the air conditioner compressor is available to you. A hot climate pilot will learn how to load passengers quickly, close the door and move swiftly through the checklist to start the right engine. If the sun is beating down on the airplane, you’ll have precious seconds before the sunrays and the greenhouse effect create a sweatbox. Seconds count. Move quickly, but deliberately.
If you have trained ground support personnel to help you, you have some other options available to cool your passengers. In this case, the pilot will move to the front left seat and start the right engine, feather the prop if desired, cool the cabin for about five minutes and then call for the passengers. The ground personnel will pull chocks, make sure everything in the back of the airplane is secure and close the door. This allows the pilot to shut off the environmental system, then quickly start the left engine and then turn the environmental system back on. It affords a cooler boarding process.
Now that both engines are running
Now that the passengers are loaded, it’s time to taxi and depart. The air conditioning works far better when the airplane is flying, so do everything possible to avoid ground delays. The best plan to beat the heat in a King Air is to get airborne quickly and climb. The cold temperatures of higher altitudes are your friend.
But if you have a longer taxi or have delays on the ground, the right condition lever can be moved to high idle, ensuring the compressor has enough speed to properly work. If you see an N1 LOW caution light, you know you have insufficient gas generator rpm to allow the air conditioner compressor to operate. For symmetry in taxiing, the left engine can also be brought to high idle. Whether both engines are in high idle, or if the right engine only is brought to high idle, all King Air models taxi well regardless of the condition lever position.
From a maintenance perspective, it is critical that you have your system topped off with refrigerant in the spring of each year. It’ll cost you a shop visit, but comfort throughout the summer will be worth the expense. We have a King Air B100 that has a supertight system that cools remarkably better than any other King Air we operate. It never leaks refrigerant and the blowers are strong. A mechanically sound system is critical to good operation and a worthy investment.
Another trick to cooling your cabin is to keep your bleed air valves in the ENVIR OFF position, ensuring no warm air from the bleed air system competes with your air conditioning system. You can start the initial climb with the bleeds in ENVIR OFF and then turn them to the OPEN position when climbing through a comfortable cabin altitude. The system will begin pressurizing normally, and I bet your passengers will never know the difference.
A reset switch in the wheel well?
Most newbies to the 3XX series learn about the small reset switch (or a circuit breaker) located in the nose landing gear wheel well to manage high-pressure trips in the compressor. This is either the best-placed switch or it is the absolute worst position for a switch. In my opinion, it is the worst. I cannot tell you how many times I’ve cursed that its location makes it inaccessible in flight. There have been many times when the air conditioning would not work, and I suspected that the switch was open. Sure enough, after the flight and after everyone came out of the airplane sweaty and stinky, I went to the nose wheel area and discovered that the switch needed to be reset.
Why did Beechcraft put that switch in the nose wheel area and not in the cockpit? My only guess is they knew pilots would use it with reckless abandon if the cabin got hot. It is so compelling to reset a circuit breaker in flight, but we all know that’s usually a bad idea. A circuit breaker pops when more current flows across that circuit than the wiring is rated, and a reset switch needs to be reset because of a problem. A real fire hazard occurs when pilots reset circuit breakers, and flipping this switch too frequently cannot be good for the system. But, when it is sweaty hot in a King Air, I know of few pilots who would have the self-restraint to not reset the reset switch incessantly.
If you fly a King Air 3XX, that reset switch in the front wheel well should be a part of every preflight. If it needs to be reset frequently after flights, be sure to have maintenance take a look.
How to operate the system for maximum coolness
I’m a huge fan of using the auto position for any switch in an airplane, regardless of which system is being considered. If you can’t remember the finer points of a particular system from your last training event and that system has an auto position on the switch, that’s probably a really good position for that switch in most flight conditions. In all King Air models, there is an AUTO position for the CABIN TEMP MODE switch, which is a convenient position for everyday use.
Tom Clements has an excellent article in the September 2020 issue of King Air magazine that details the internal operation of the environmental system. My favorite part is his articulation of how the bypass valves act like a water faucet in your house. You mix hot and cold water to get the exact temperature you desire from your faucet. Similarly, in the King Air you have bleed air (hot) and cooler ambient air (cold) controlled by two bypass valves to achieve the desired incoming cabin temperature.
If you operate in the AUTO position, then you can adjust cabin temperature using the enabled CABIN TEMP rheostat. Turning this switch fully counterclockwise usually activates the compressor and moves the bypass valves fully cold. This is not a bad way to get maximum cabin cooling, but if the system’s automatic functioning is not working precisely (which is a distinct possibility), the bypass valves may not be fully cold. If this is suspected, you should operate in manual mode.
Manual mode confusingly has two positions: MAN COOL and MAN HEAT. The only appreciable difference (as applies to the discussion of cooling the cabin) is that MAN COOL enables the air conditioner compressor. If you suspect you are not getting maximum cooling, move the CABIN TEMP MODE switch to MAN COOL and hold the MANUAL TEMP INCR/DECR switch to the DECR (decrease) position for 30 seconds or more. By doing this you are driving both bypass valves to the maximum cooling position and activating the air conditioning compressor, which gives you maximum cooling.
On a hot day I begin a flight operating in MAN COOL and holding the MANUAL TEMP switch to DECR for more than 30 seconds. This way I know the system is set to provide air that is as cool as possible. Then, in flight at higher altitude, I’ll move to the AUTO position and regulate temperature with the rheostat.
There are several fans that move air in the King Air and you want them turning as fast as possible. If it is hot in the cabin, make sure the AFT BLOWER is ON and the VENT BLOWER is in the HIGH position. This moves the most air and provides the best cooling.
There is more nuance to the system, of course, but the strategy shared in this column ensures you’re operating the environmental system for maximum coolness.
You don’t want to be known in your friend circle as “the pilot who is not happy until everyone else is not happy.” Put some of these ideas into practice on your next hot weather flight and see if you can make a cooler cabin for your passengers.