Preliminary Details of a Helicopter Crash in New Jersey
I don’t normally write an article based on a preliminary report; however, this one made me sit back in my chair.
On the 4th of June 2022, a Bell 407GXP helicopter, registration N98ZA, crashed near Fairfield, New Jersey.
The Bell 407 is a single-engine helicopter with a four-blade “soft-in-plane” design rotor, which means that it is an articulating rotor system with a composite yoke attached the mast. The Bell 407GXP in the accident was built in 2015 and powered by an Allison Model 250 turboshaft engine.
The helicopter was on a positioning flight from Essex County Airport (CDW) in Caldwell, New Jersey to John F. Kennedy International Airport (JFK) in New York. Only the pilot was on board; local media reported that he was travelling to New York to pick up a customer for a charter flight.
At 11:47 that morning, the helicopter departed Essex County Airport, which has an elevation of 53 metres or about 175 feet above mean sea level (amsl). The weather was clear. The pilot climbed to about 500 feet amsl and flew south-east.
About two miles south of Teterboro Airport, the pilot contacted ATC and asked for a return to Essex County. He said no when the controller asked if he needed assistance. He must not have been very concerned, as he said no when the controller asked if he needed assistance and reversed course back to Essex rather than land at Teterboro. At Essex, the pilot was cleared to land on runway 28.
The helicopter crossed the runway threshold flying at 33 knots groundspeed at 150 feet amsl (so about 25 feet over the runway). It continued at that altitude and groundspeed for about ten seconds, then slowed down as the nose pitched upwards to climb away, turning slightly to the right.
A CCTV camera at the airport showed that the nose of the helicopter yawed to the right as the helicopter slowed. Something was wrong.
In normal operation, the main rotor mast connects the transmission to the rotor assembly, rotating the upper plate and the blades using the power from the engine.
Instead, the helicopter began rotating around the main rotor mast.
An eyewitness said the Bell 407 was about 100 to 150 feet in the air when it began to spin and then crashed into the grass at the edge of the airport.
From the report:
Seconds into the vertical descent, the right yaw slowed, stopped, and the helicopter rotated to its left for the remainder of the vertical descent to ground contact. After ground contact, the main rotor continued to turn and the main rotor blades continued to strike the ground, ultimately shedding about 50 percent of the span of each blade.
Thirteen minutes had elapsed since the helicopter had taken off.
You can hear the ATC Audio after the crash on this video from FX Aviation. Note the images were added for effect and are not of the accident helicopter.
Rescuers found the pilot still in the pilot seat, partially leaning out of the cockpit. He had obviously suffered severe head injuries. The helicopter fuselage and tail boom were substantially damaged.
An examination of the wreckage found that the tail rotor crosshead drive plate, which should have been bolted to the tail rotor crosshead, was not attached. It should have been bolted in with two bolts. There were no bolts on the scene and no fragments found the threading. In fact, the threads where the bolts should have been screwed in were completely undamaged: there was no trace of the bolts or any deformation or cross-threading.
The breaks on the rotor blades showed that the main rotor flight control had been connected to the cockpit controls at the time of impact. Similarly, breaks to the tail rotor gearbox and pitch control road showed that tail rotor control had still been connected to the pedals.
Moving the “pitch change push-pull tube” correctly moved the pitch change rod. When the pitch change rod moved, the attached tail rotor crosshead drive plate moved, but without moving the crosshead, which should have been attached with those two missing bolts.
The Bell 407GXP had undergone maintenance the day before, which included the installation of the tail rotor.
The director of maintenance said that before the installation, he prepared the tail rotor assembly by laying all of the parts out on a maintenance cart. He installed the tail rotor assembly and asked a mechanic to verify the mast nut torque.
It would seem that the investigators were not convinced by the director’s use of the terms “finished” and “verified”.
He then “finished” the installation and had another “verify” the work.
I’m not sure I’ve seen a report use quote marks to denote possible untruths before.
A company pilot completed a preflight inspection of the helicopter and performed “ground functional checks” and three consecutive maintenance runs to affect balancing of the tail rotor.
The director of maintenance admitted that after the mast nut torque application, he was called away to consult on other repairs, and then came back to complete the installation. He wasn’t sure how long he was away.
The NTSB is continuing the investigation under accident number ERA22FA257, with supporting staff from the FAA and from Rolls Royce, who acquired the Allison Engine Company in 1995.