Moments before a jet carrying a University of Michigan organ transplant team crashed into Lake Michigan, the pilot reported having trouble controlling the plane, a National Transportation Safety Board official said Tuesday.
In the distress signal, the pilot said he was experiencing "trim runaway," a situation where the plane pulls severely in one direction, often upward or downward.
As firefighters and medical personnel continued the grim recovery process near Milwaukee on Tuesday, the NTSB arrived at the scene to begin its exhaustive investigation into what went wrong.
That probe is expected to take months, leaving many unanswered questions as family members of the six men on board mourn. The crew - two U-M doctors, two transport specialists and two pilots - was en route back to Willow Run Airport with organs for a transplant surgery when the Cessna 550 Citation went down.
NTSB senior air safety investigator John Brannen said the audio between the tower and the pilot showed that he reported a problem with the trim system, but Brannen said he doesn't know what could have caused the problem. Trim runaway has previously caused accidents, he said.
"We will piece together what we can of the wreckage," Brannen said.
The NTSB planned to look at the aircraft's maintenance records within the next few days. The fuselage and cockpit voice recorder - which could be vital to reconstructing the crash - had not been located, Brannen said.
Brannen said it's unlikely weather and pilot error were factors in the crash.
Later Tuesday, the underwater recovery process was suspended because of four- to six-foot swells, officials said. Two search vessels would remain out Tuesday night, and divers were scheduled to return to work Wednesday.
Officials said some human remains and debris from the plane have been located.
Milwaukee County Medical Examiner Jeffrey Jentzen said he likely would have to use dental records and DNA to identify the victims.
Keith Holloway, a NTSB spokesman, said the on-scene investigation will continue until the pieces of the plane have been assembled. It will then take another five to 10 days for a preliminary report with more detailed facts to be issued, he said. A cause - which involves collecting extensive records on maintenance, pilot training and conditions - may not be declared for 12 to 18 months.
Trim runaway
Aviation experts say that although trim runaway has caused accidents in the past, it's likely there were additional factors - such as problems with the tail of the plane.
"Trim" refers to the devices that help control the plane's ability to climb, descend or maintain level flight. When it is in "runaway" condition, it could unexpectedly push the plane into a dive, a steep climb that could stall the jet, or force it to bank heavily in one direction. It can be caused by a variety of factors, ranging from pilot error to mechanical failure.
Erik Rigler, a New Mexico aviation accident investigator and reconstruction specialist, said he expects the crash was caused by more serious problems than trim runaway.
Rigler, who has extensive experience with the Cessna Citation, said the horizontal stabilizer - a key portion of the tail of the plane - may have fallen off, creating a similar reaction as trim runaway.
Rigler said pilots are trained to control trim runaway in as many as nine different ways - such as shutting off the jet's electrical systems, which wouldn't effect the engines.
Inspections of maintenance records on the jet could provide important clues to what happened, Rigler said. He noted if maintenance involving the controls occurred within the past few days, it would "heighten suspicion."
"Not all the investigation is going on at the bottom of Lake Michigan," Rigler said.
Ross "Rusty" Aimer, CEO of Aviation Experts in California, also said the theory of a problem with the tail is a strong hypothesis to explain the crash. He said a pilot would not have known if he lost a portion of the jet's tail.
"There are many ways to control runaway trim," Aimer said. "If the tail dropped off, there is absolutely no way to control that airplane."
Larry Grandy, of Aviation Accident Consultants in California, said it's unusual for trim runaway alone to cause plane crashes.
"It could be a bunch of things," Grandy said. "It could be he (the pilot) thought it was that and it was something else. They won't know until they pull that (plane) out of the water."
According to NTSB records, trim runaway was blamed for the July 22, 2003, crash of a Cessna Citation 525 jet that plunged into the waters of Penn Cove in Coupeville, Wash. In that crash, the pilot reported the plane suddenly pitched to nose-down position and the electric trim would not respond to inputs from the control wheel trim switch. The pilot and a passenger were not injured.
Transport crashes
The Cessna Citation was leased by the U-M Health System and chartered by Marlin Air.
In the lobby of Marlin Air, based at Willow Run Airport, family members of the pilots watched televised coverage Tuesday afternoon but declined to speak to a reporter. A Marlin Air employee who would not give his name said both pilots were highly qualified, veteran aviators.