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Energy managementEnergy management

To deal with an emergency, you must understand exactly what takes priority. 

Emergency response could be described as involving two phases: immediate and slightly less immediate.  There are things that must be done now to stabilize the situation, if possible. Other urgent priorities can’t be addressed until that’s been accomplished. Losing track of this hierarchy invites grief, but it’s easily done during an adrenaline rush. That fact often rears its ugly head after engine failures, when the desire to get the aircraft back to the runway can obscure the utter necessity of keeping it under control.

Losses of power continue to trigger fatal low-altitude stalls when pilots forget to place top priority on keeping the wings flying. It happens in twin-engine airplanes as well as in singles, even twins whose operating manuals claim they are capable of climbing out and returning to land. But just as single-engine pilots have only a few seconds to lower the nose after losing thrust, continuing a climbout in a light twin that’s lost an engine requires urgent attention to preserving enough airflow to maintain control authority while reducing drag to the absolute minimum. Attempting to turn back without cleaning up the airframe, feathering the windmilling prop, and climbing to a safe altitude is a low-percentage bet.

In the past few years, a series of spectacular accidents have demonstrated the precarious energy balance inherent in asymmetric thrust at low airspeed and a high angle of attack. One took place in Hammond, Louisiana, on Oct. 14, 2015. The airplane was a Cessna 421B with just two on board, a professional pilot and his employer, owner of an aircraft brokerage and management business. At 3:36 p.m., the pilot received and read back an IFR clearance to Atlanta at a filed altitude of 17,000 feet. Two minutes later, he advised that he was ready to taxi and was cleared to taxi to Runway 31.  About one minute after reaching the threshold, the Golden Eagle received its takeoff clearance.

At least three witnesses on the ground saw the twin Cessna start its takeoff roll and lift off. Just over halfway down the 6,502-foot runway, at an altitude of no more than 100 feet, it made “a popping noise,” the right propeller slowed visibly, and the airplane began to yaw to the right as its pilot responded with left rudder. The tower controller heard but did not initially process the pilot’s next radio call—“Mayday, mayday, mayday, we gotta come back right away”—and asked him to say again before clearing him to land on Runway 18. The pilot’s final two transmissions were unreadable.

All four witnesses saw the Cessna initiate a right turn—toward the bad engine, whose prop was still windmilling. It cleared a line of trees by perhaps 150 feet before the right wing dropped and the nose fell to an attitude of about 60-degrees nose down. A “massive fireball” consumed the airplane after impact.

During teardown, investigators found that several of the nuts that should have secured the studs joining the right engine’s crankcase halves were loose. The loose studs had allowed the No. 2 main bearing to spin out of place, causing the crankshaft to fracture. All six cylinders appeared to be new, and while the airplane’s logbooks were apparently on board and destroyed by the fire, investigators eventually obtained service records from two of the facilities that had maintained the aircraft. At its last annual inspection, eight months and at least 30 flight hours before the accident, all the cylinders had been replaced with overhauled units—a job that required removing the nuts from the crankcase through-studs.

The NTSB concluded that “maintenance personnel's failure to properly tighten the crankcase through-studs during cylinder replacement … led to crankshaft fracture,” precipitating the accident. But they also cited “the pilot's failure to feather the propeller on the right engine and his failure to maintain control of the twin-engine airplane while maneuvering to return to the airport.”

It’s not clear why the pilot didn’t close both throttles and settle back onto Runway 31. Perhaps he didn’t feel he had enough room to avoid an overrun, though there’s at least 1,000 feet between the departure threshold and the nearest obstruction. It’s also not entirely certain that the initial right turn was deliberate and not the first manifestation of a loss of directional control as airspeed decayed below VMC. What’s indisputable is that before attempting to turn in either direction, he needed to neutralize the drag of the windmilling prop, keep the nose down long enough to build airspeed, and climb to an altitude that offered some margin for error. Getting further from the runway would have been the necessary first step toward making it back again.


ASI Staff

David Jack Kenny

David Jack Kenny is a freelance aviation writer.
Topics: Multiengine, Piston, Accident

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