The National Transportation Safety Board and Federal Aviation Administration are investigating a helicopter crash that killed two people and critically injured one other in Seattle on Tuesday.
While there is no official word yet on what caused the crash, some aviation analysts suspect the crash could have been the result of an engine problem.
“It sounds like from the reports that there was a crash on takeoff, which makes you immediately think about an engine failure,” says aviation attorney Alisa Brodkowitz.
Brodkowitz tells KIRO Radio’s Tom and Curley Show that the helicopter was a Bell 407 and for the aircraft to even be certified, it had to be able to land without engine power.
“You have got to be able to land this when your engine is out,” says Brodkowitz.
A pilot trying to land without power, Brodkowitz explains, goes into something called auto-rotation in an attempt “float” down safely.
“When a helicopter is flying, the air actually moves from above the helicopter down through the rotors so you’re pulling air from above down. When you lose your engine, you can’t do that anymore, so you have to auto-rotate.
“Auto-rotating is when you turn the blades so they have a negative pitch and you’re able to let air move up through those rotors from the ground up, and then the aircraft basically floats to the ground,” says Brodkowitz. “In order to do that, you have to have a certain amount of energy.”
Problems can occur, Brodkowitz says, if the aircraft is in something called the “dead man’s curve.”
“That is a height-velocity curve which tells us how much height you need to have and how much airspeed you need to have in order to land under these conditions.”
The dead man’s curve is something that appears in all flight manuals for helicopters, says Brodkowitz.
“It’s literally a shaded-in area where on one edge you have the height off the surface of the ground, and on the other plane you have your airspeed or how many knots,” says Brodkowitz. “In between there, it’s shaded in and they say don’t operate in the shaded-in area.”
Estimating Fisher Plaza’s helicopter pad at around 60 feet off the ground, and looking at a manual for a similar type of helicopter, a Bell Jet Ranger 206, Brodkowitz tried to estimate the amount of speed the helicopter would have had to have to avoid the dead man’s curve.
“For this aircraft,” says Brodkowitz. “If you’re 60 feet above the ground, you need about 45 knots in terms of air speed to be out of the dead man’s curve.”
Had there been reports from eyewitnesses of portions of the blades flying off the helicopter, Brodkowitz says then it might point to a different cause.
“What you’ll find is parts of the blade far from the helicopter,” says Brodkowitz. “If we were to find that, then that would indicate a blade failure.”
The NTSB is on site continuing the investigation. They reportedly will move the helicopter from the crash scene Tuesday afternoon. Seattle Police are asking people to stay away from the area as the investigation continues.