Comair Flight 3272 may have been flying so slowly as it approached Detroit Metro Airport that it may have stalled when pilots attempted to turn the commuter aircraft.
Data gleaned by the National Transportation Safety Board (NTSB) from the Embraer Brasilia 120 twin-engine turboprop plane's data recorder revealed it was flying close to the aircraft's stall speed.
That means air couldn't have moved fast enough over the wings to generate lift,
a federal investigator told the Detroit News on Tuesday.
Other conditions revealed by the recorder have led NTSB investigators and other experts to suggest that Capt. Dann Carlsen and First Officer Kenneth Reece may have inadvertently stalled the plane in midair. Key among those findings is that the plane's shaker stick, a warning device in the controls, began vibrating in the pilot's hand.
''When the shaker stick is engaged, that's a very high probability that the engine has stalled,'' said Robert Watson, a retired NTSB investigator who probed 679 crashes during a career spanning two decades.
''Since they were banking (turning) the airplane already, it's hard to generate any additional speed and lift,'' he said. ''I wouldn't be surprised if there was ice on the wings, too, because when you have a stall with ice, you have the abrupt drop like that Comair plane had.''
Even a little ice could have brought the plane down under those conditions, said experts.
''It wouldn't take much ice to push them over the edge,'' Chuck Eastlake, an aeronautical engineering professor at Embry-Riddle Aeronautical University in Daytona Beach, Fla., said in an interview with the News. ''A little bit of ice was possible and definitely could be a contributing factor in a marginal situation.''
Mr. Watson, Mr. Eastlake and others base their observations on the flight recorder for the final 38 seconds of the Cincinnati-to-Detroit flight. The information was released by the NTSB on Monday.
The plane's data recorder shows it was flying at about 189 mph with its power at idle when it entered a 30-degree turn, left wing down, which in a few seconds increased to a steeper 40 degrees. Within 16 seconds, the speed had dropped to about 167 mph. The stall speed under ideal flying conditions for the Embraer 120 is about 161 mph for a 45-degree turn, Mr. Eastlake said.
Icing could dramatically increase the stall speed, meaning the plane would have to fly faster to stay aloft.
The crash on Thursday afternoon in a Monroe County field killed all 26 passengers and three crew members. At the time, a cold front was pushing through the area with 14-degree temperatures and blowing snow.
Other pilots at the time were reporting icing conditions.
A top official with another large commuter airline that flies Embraer 120s said that under those weather conditions, his pilots are ordered to maintain a minimum speed of 184 mph, at least 17 mph faster than the Comair plane was flying when it appeared to stall.
The air speed and other indicators are data collected by the NTSB. An investigation, expected to take about a year, will determine whether pilot error, ice or other factors caused the crash. Often, a combination of factors contribute to a crash.
''Ice is not necessarily the main player,'' said one source. ''But there is a lot of work to finish.''
Comair had no comment on the report that the plane may have stalled because it was going too slowly.
A former Comair pilot, said it's hard for him to believe the crew would have stalled the aircraft. He said they were too experienced to knowingly fly that close to stall speed.
Mr. Murphey said that it's standard procedure to add between 10 and 25 mph to the stall speed when encountering potentially bad weather.
''You're better off erring on that side,'' said Mr. Murphey, who now flies DC-10s for a major carrier.
In other developments Tuesday:
- Comair Inc. confirmed that the plane's right engine was replaced on Jan. 4 during routine maintenance. The airline usually replaces engines when they have gone 11,500 hours, said Meghan Glynn, Comair's media relations manager. The plane's left engine was replaced in June after an object damaged compressor blades.
- Monroe County medical examiner Dr. David Lieberman said remains of all 29 victims were recovered, and 21 had been identified.
- The warmer weather and clearer skies made it easier for the NTSB to gather wreckage. Over the weekend, bitter cold and high winds forced NTSB investigators and volunteers to work 15- to 20-minute shifts.
PROFILES OF VICTIMS
SIX DAYS OF CRASH COVERAGE
