Expert says ice on wings only reasonable explanation for crash
OTTAWA (AP) _ The head of the probe into the crash of an Arrow Air military charter said Wednesday that probers had eliminated only one possible cause - an explosion - for the disaster last December that killed 248 U.S. soldiers.
Earlier in the day, Ralph Brumby, representing the maker of the DC-8, told the Canadian Aviation Safety Board hearing that ice sticking to the wings is the only reasonable explanation for the crash of the jetliner on takeoff at Gander, Newfoundland.
Board chairman Bernard Deschenes told reporters at the close of the last day of hearings that he was very interested in Brumby’s analysis, but was not ready to endorse ice as the principal cause.
Deschenes said investigators would make careful comparisons of the Arrow crash with records of others known to have been caused by ice.
Of many possible causes being looked into, the only one the board is ready to discard is the theory that an explosion - whether by accident or sabotage - brought down the plane, Deschenes said. He said he thought it was important to clear the air by eliminating terrorism as a consideration in the Gander crash.
Brumby, a McDonnell Douglas Corp. expert on DC-8 design and performance, testified that any contamination on a wing’s forward edge dramatically decreases lift and increases drag.
″A very small amount of roughness, as little as medium-coarse sandpaper, will increase the stall speed by as much as 20 (percent) to 30 percent,″ he said.
The Arrow Air plane, which carried eight crew members and 248 soldiers returning from peacekeeping duty in the Sinai peninsula, crashed Dec. 12 less than a minute after taking off from Gander. All aboard were killed.
Previous testimony in seven days of hearings revealed there was freezing drizzle while the DC-8 was in Gander, but none of the witnesses said they saw ice on the wings.
Brumby said he and other company specialists looked into many other suggested causes for the crash, but, ″I haven’t found a reasonable explanation that will develop the flight path″ recorded in the plane that crashed.
The safety board, which still is considering such other possible causes as engine failure, and pilot error, is expected to issue a report later this year.
Brumby said the flight data recorder recovered from the Arrow Air wreckage showed a takeoff remarkably similar to others in which ice or snow on the wings was blamed for crashes.
Data from the recorder suggest that the DC-8 reached an adequate takeoff speed but had trouble lifting off and stalled at a speed of about 160 knots, Brumby said.
Under the conditions at Gander that morning, the normal stall speed for the plane would be 138 knots, he testified.
According to Brumby, the important factor in determining ice effects is the roughness created on the wings’ leading edges, not the total amount of ice.
″The kind of roughness that we think would cause this kind of stall is four-hundredths of an inch,″ he said.
There was light freezing drizzle when the plane landed in Gander, but it soon stopped and there was no precipitation during the takeoff just before dawn.
The plane began the flight in Cairo, with fuel stops in Cologne, West Germany, and Gander on the way to Fort Campbell, Ky., where the troops from the 101st Airborne Division were based.
The plane’s flight engineer was seen making a normal pre-flight inspection of the plane during the Gander stop, and presumably would check for ice on the wings. The pilot did not request a de-icing, but investigators have not yet been able to determine whether ice was present.
″There is no direct physical evidence, only the weather at the time,″ Brumby said. The conditions were similar to during other accidents caused by icing, he said.
After takeoff, the plane banked to the right and then veered in that direction, losing altitude until it smashed into a rocky hillside beside Gander Lake.
Brumby said that suggested ice conditions were slightly worse on the right wing than the left, making that wing stall sooner.