May 30—Emergency responders at the Mercy Flight crash that killed two pilots on April 26 in Elba have known that the Bell 429 helicopter landed in two pieces: the main body and the tail.
Now a preliminary report released last week into the crash that killed pilot James E. Sauer and Stewart M. Dietrick, a Bell helicopter flight instructor, provides a sense of how such a split could have happened. The report from the National Transportation Safety Board noted a fracture in the tail "consistent with main rotor blade contact."
When main rotors — which spin above the helicopter to lift and push it forward — flex or dip down and essentially slice the helicopter in two while in midair, it's called a tail-boom strike. The back of the tail-boom section of the wreckage was found "largely intact" 390 feet from the main wreckage, according to the report, but a third piece, comprising a small part of the tail boom and the tail rotor drive shaft, was found by investigators 1,620 feet away.
The "angled fracture" in this smaller piece of the tail boom — unmentioned in initial reports — showed evidence of contact with the main rotor, the report said. The drive shaft, also included in that fragment, works with the tail rotor gearbox to balance the speeds of the main rotors and the tail rotors, keeping the helicopter from spinning out of control.
If the tail boom is cut away from the rest of the helicopter, the pilot loses control.
The NTSB did not determine a specific cause for the crash that occurred on the instructional flight and likely will not for another year or two, an NTSB spokesperson confirmed.
"Investigators are still many months away from starting the analysis," said Peter C. Knudsen of NTSB media relations.
Generally, the major causes of helicopter crashes are human error, mechanical problems or environmental factors, or a combination of the three, according to pilotinstitute.com, a pilot education site.
But just because there's a clearer idea of how the helicopter came apart does not necessarily pinpoint a cause, said Ron Goldman, a Los Angeles-based attorney not involved in the Mercy Flight case but experienced in helicopter crash lawsuits. Goldman previously said he thought, given the experience of the two pilots, a mechanical explanation for the crash was likely; he doubled down last week.
"There are very suspicious earmarks of mechanical failure," Goldman said after reading the report.
Richard P. Amico, chief trial counsel for the Barnes Firm, agreed. "It appears the attention of the report was on the failure of a mechanical system and not on the action of the pilots."
One challenge facing investigators is piecing together the crash timeline. What training exercises were the pilots practicing? What kind of malfunction, if any, caused the aircraft to descend unexpectedly? What damage happened as a result of the helicopter's impact with the ground?
This is not an easy puzzle to solve, but it's important. "If this is a repetitive failure, you don't want it to happen again," Amico said.
Witness accounts cited in the report support the tail-boom strike theory but help little with the cause. Each witness describes a loud noise occurring in the air before the helicopter crashed to the ground.
One described the helicopter as "almost stationary" in the air prior to a loud bang heard as it began to fly away before its unexpected descent. A second described the aircraft as "hovering" before "it fell apart," and a third said the helicopter's noises were a series of "whoosh" sounds before "three loud and rapid cracks."
A tail rotor malfunction could cause the pilot to lose control of the aircraft; the tail rotor's purpose is to counteract the torque of the main rotor, acting essentially as a balancing mechanism. If the tail rotor system is compromised, the helicopter is "just a rock spinning under a rotor blade," Goldman said.
The NTSB report did not specifically mention the pitch link control, the Bell 429 helicopter tail rotor part the Federal Aviation Administration had published a directive about on the same day as the Elba crash, but a broken pitch link has caused pilots to lose control.
"That's something the NTSB will look hard at, no question," Amico said in regard to the April 26 Airworthiness Directive.
If it were his client, Goldman said he would ask for a close examination of the tail rotor system, including the gearbox, which acts as the aircraft's transmission. Goldman emphasized the concern regarding the tail rotor is the stress and vibrations it endures relative to its size and the resulting wear and tear it experiences over the course of hundreds of flight hours, hence the FAA's frequent directives for maintenance.
Neither lawyer was convinced that the tail rotor was the culprit, however.
"The tail rotor can be one of many problems," Amico said. "Often there's more than one problem that results in a crash."
"It could have been the main rotor system," Goldman said, "since the blades had to drop down. But how did they get there? It was still generating power."
It's noteworthy that two witnesses said the helicopter hovered prior to its crash. Compared to when a helicopter accelerates, the main rotor blades' revolutions per minute (RPMs) decrease while hovering, which could cause them to droop. The FAA's 27-page chapter on emergencies and hazards for helicopters describes a scenario of a tail-boom strike caused by dangerously low main rotor RPMs.
"As the helicopter begins to descend, the upward flow of air acting on the bottom surfaces of the tail boom and any horizontal stabilizers tend to pitch the aircraft nose down. These two effects, combined with any aft cyclic by the pilot attempting to keep the aircraft level, allow the rotor blades to blow back and contact the tail boom, in some cases actually severing the tail boom. Since the tail rotor is geared to the main rotor, in many helicopters the loss of main rotor rpm also causes a significant loss of tail rotor thrust and a corresponding loss of directional control."
Neither engines nor controls seemed to be the culprit for the crash, according to the report.
The report said the flight occurred during VMR, or Visual Meteorological Conditions, a category for safe flying that means pilot visibility exceeds 5 miles and the ceiling, or distance between the ground and the first layer of clouds, is more than 3,000 feet. With visibility at 10 miles, winds at 11 mph and cloud cover at 3,400 feet, weather likely did not factor into the crash.
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