Most C-90 pilots understand the sequence of events that transpire in the event of a boost pump failure. A red fuel pressure light illuminates and is quickly extinguished as the cross feed opens automatically allowing the functioning electric boost pump to supply fuel pressure to both high pressure engine driven pumps.  This eliminates the possibility of cavitation of the high pressure pump due to suction feeding.  It also prevents engine surging at high power settings and negates the need to record any time against the 10 hour overhaul requirement of the high pressure pump during suction feed operation. So far, so good. Of course, since we are talking about a King Air, there is more to the story. Did you know that boost pump failure can lead to engine failure? Here’s how:

Boost pump failure during a rapid climb-out will cause a gradual power loss on the affected engine starting  at approximately 13,000 feet. This altitude varies with the fuel temperature in the tank. A higher fuel temperature will cause a gradual power loss at a lower altitude. Interestingly, a complete power loss will occur if the climb is continued under these circumstances. This power loss results from the highly aerated condition of the fuel caused by rapidly decreasing tank pressure during a rapid climb. This allows the air trapped in the fuel to expand. However, once the fuel tank pressure has stabilized and excess air has escaped from the fuel, the loss of a boost pump has less effect on the engine operation at maximum power settings.  It is impossible to determine how much time is required to stabilize the fuel from the highly aerated condition because it is a function of both rate of climb and fuel temperature. Fuel stabilization should occur after a few minutes of stabilized cruising operation. If in doubt, open the crossfeed! Descents from a high altitude with the boost pump inoperative do not affect engine operation.

Q: I live in Florida. How often should I do a compressor wash on my PT-6?

A: Pratt & Whitney recommend that you do a compressor wash at least once a week if the airplane is exposed to occasional salt air.

I recently trained a student that experienced an interesting event while flying an E-90. While cruising at FL210, the upper door latch failed from fatigue. The upper portion of the door opened about six inches resulting in an explosive decompression. The pilot stated one of the more unusual aspects of the rapid loss of cabin pressure was the amount of dirt and sand that was sucked out of the carpet. The airplane was a 1972 model with approximately 10,000 hours. As the King Air fleet ages, it’s important to thoroughly preflight the airplane. On older models, pay particular attention to the door pin brackets and the possibility of fatigue cracks.

QUESTION: Are there any split flap procedures on the C-90?

ANSWER: I get this question frequently in ground school. There are no emergency procedures for a split flap situation. If the wing flaps are inoperative, the airplane should be landed in the existing flap configuration. If you have a flap malfunction, ensure flap position is visually inspected prior to resetting the flap handle to the previous position. Once reset, the flap motor CB should be pulled to prevent inadvertent flap movement. It should be noted that the military flight tested the aircraft under all possible asymmetric flap configurations and found the airplane to be fully controllable.

Prist does not kill fuel microbes. Although the King air rarely experiences fuel system icing, many pilots order Prist when re-fueling in the mistaken belief that any microbial growth in the tanks will be killed. Prist is a Biostat. A Biostat can keep an outbreak of microbes from continuing to grow, but it won’t kill them. Only a Biocide can eradicate growth in fuel tanks. How do you know that you have growth in your fuel tanks? The signs can vary. Obviously clogged filters, contaminated tank bottoms, or fuel samples that have green or brown slimy formations are all definitive signs of bacterial growth. Untreated, this problem can lead to corrosion and damage to the structural integrity of the airplane. Of course, the worst-case scenario is the loss of an airplane due to engine failure. So, what exactly are these microbes? The scientific names for organisms that live in jet fuel are Cladosporium Resinae and Pseudomonas Aeruqinosa. I doubt, however, these names will catch on with King Air pilots. These microbes live and multiply in the water found in jet fuel. By living in the water, they can feed off the hydrocarbons in the fuel. As they grow, they form dark colored mats that appear gel – like. Their waste products include acids, sludge and water. Not content with feeding off of just hydrocarbons, they also consume rubber gaskets, hoses, tank linings, and O-rings. Pilots should be aware of the signs of microbial growth in their airplanes. If growth is suspected a microbial detector kit is the most effective way to test for microbial infestation. If an infestation is present, a Biocide can eradicate the growth. Fortunately for those pilots that rarely sump their fuel tanks, most FBO’s treat their stored fuel with a Biocide prior to selling it.