Faulty Assumptions: The Fuel You Think You Have

Fuel planning is only as good as the number you start with. If the starting number is wrong, every calculation after it is wrong too, and the airplane will tell you at the worst possible time.

The AOPA Air Safety Institute (ASI) re-creates this flight in its video "Accident Case Study: Faulty Assumptions," which you can watch below. The summary that follows is ours and is based on the NTSB final report (CEN19FA124), which also gives the official probable cause. Watch the full case study for ASI's own analysis.

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The flight, in short

On April 22, 2019, a 65-year-old airline transport pilot left West Houston Airport (IWS) in a Beech 58 Baron on an IFR flight plan to Kerrville, Texas (ERV) with five passengers. His filed flight plan showed a minimum fuel load of 58 gallons, a figure that didn't account for the instrument approach or an alternate. His own planning log showed only 50 or 54 gallons aboard. The NTSB found the airplane was over its maximum gross weight even with 50 gallons, and said the pilot likely didn't want to add more.

The real number was lower. Eight days and five flights earlier, the airplane had been fueled at his request but not completely filled. He wasn't there for the fueling and didn't cross-check the receipt against his logs, so the error carried through every flight after it. The NTSB estimated about 38 gallons were aboard at takeoff. Faulty fuel quantity transmitters would have made each wing gauge read about 5 gallons high, which may have seemed to confirm the pilot's numbers.

On the GPS approach to Kerrville, with a ceiling around 1,200 feet at the airport, both engines lost power within 10 seconds of each other. The left engine came back about 40 seconds later. The pilot didn't feather the right propeller or make sure the flaps were up, as the manufacturer's engine out procedure calls for. Below the clouds at about 500 feet above the ground, the airspeed dropped below the minimum control speed and the airplane entered a right spin. All six people aboard were killed.

The NTSB determined the probable cause to be: “The pilot's inadequate preflight fuel planning and fuel management, which resulted in a loss of engine power due to fuel exhaustion. Also causal was the pilot's failure to follow the one-engine inoperative checklist and maintain the airplane's minimum controllable airspeed by properly configuring the airplane, which resulted in a loss of airplane controllability.”

Why verifying fuel matters

The NTSB found a chain of small errors on the ground: a fueling that wasn't recorded right, a fuel load that wasn't verified, gauges that read high and a decision to leave on too little fuel in an overweight airplane. Any one of them caught before takeoff would have broken the chain.

• Verify fuel with your eyes or a dipstick before every flight. Don't carry a number forward from a log.
• Match every fuel receipt to your records, especially when you weren't there for the fueling.
• Plan IFR fuel for the approach, the missed approach and the alternate, plus your reserve.
• In a twin, know the engine out procedure by memory and practice it, because the airplane gives you seconds, not minutes.