Crash Inquiry Studies Ice Buildup on Wings : U.S. Safety Board Tells of Its Earlier Concerns About Older-Model DC-9s’ Vulnerability to Cold

Ice accumulating on the wings became a central focus Tuesday as federal investigators tried to determine why a Continental Airlines jetliner crashed on takeoff during a snowstorm Sunday, killing 27.

The plane was a DC-9 Model 10 built in 1966. National Transportation Safety Board Chairman Jim Burnett said the board’s staff had noted months ago that such older-model DC-9s are especially vulnerable to icing, because of their wing design.

The early models were built without “slats,” surface extensions of the leading edge of the wings that give added lift on takeoff. Slats were added on later models.

Crew Is Another Focus

Burnett, in a later briefing Tuesday night, suggested that the crew was not as experienced as had been reported.

He said that Capt. Frank Zvonek, 43, of Carlsbad, Calif., had only 33 hours as a captain of a DC-9, and that First Officer Lee Bruecher, 26, of Houston, had just over 36 hours in a DC-9. However, he refused to characterize the two as “inexperienced.”

Burnett, in previous testimony before a congressional panel, recommended that captains and first officers with relatively little experience not be paired in a cockpit. He said also that Zvonek’s scheduled certification on Oct. 19 as a DC-9 pilot had been delayed at the request of a Continental flight tester.

The tester, Burnett said, recommended additional operational training for Zvonek before certification. Zvonek was certified on Oct. 28.

Burnett also referred to an “unusual sequence of events” as the plane moved from the gate to the icing pad and to the takeoff position, saying that it was not in accordance with “normal” procedures.

Flight 1713 sought and received permission from the airport control tower to taxi from the pad, where it was de-iced, to the takeoff position at 1:51 p.m.

However, according to Burnett, the pilot did not ask for permission to taxi from the gate to the pad. When the plane was at the pad, the control tower believed it was still at the gate. Consequently, the control tower was one step behind the plane.

In the process, at least one plane had been put in front of Flight 1713, adding to the takeoff delay and perhaps aggravating the icing problem.

And because of the windy, snowy weather, operations at Stapleton were delayed, and the plane did not receive clearance for takeoff until 23 minutes later, at 2:14 p.m.

Whether the pilot checked visually during that period to see if ice was accumulating on the aircraft is not yet known.

Three Accidents Cited

There have been at least three DC-9 accidents in recent years in which icing was found to be a contributing factor.

Burnett also said that the plane involved in Sunday’s ill-fated Flight 1713 had waited on the ground in subfreezing temperatures for more than 20 minutes after de-icing before the takeoff attempt was made.

He noted that the board at one time had considered recommending that icing checks be made at intervals of no more than 20 minutes.

Continental said Tuesday that such checks are made at 20-minute intervals as a matter of company and Federal Aviation Administration policy, but, as yet, there has been no confirmation that the cockpit crew of Flight 1713 actually kept to that schedule.

Pilot Makes Determination

FAA requirements state simply that a pilot must determine that his plane is free of ice before attempting a takeoff in inclement weather, without specifying how that is to be acomplished.

While the NTSB continues to stress that it is too early to speculate, aviation experts say that icing could account for the way the Continental jetliner apparently stalled as it attempted to take off on a scheduled flight to Boise, Ida., with 82 aboard.

Witnesses said that the plane veered right, then left, then right again as it lifted off from Stapleton International Airport’s Runway 35 Left.

The witnesses said they thought the right wing was the first part of the plane to hit the ground, but Burnett said Tuesday that records show it was actually the left wing.

The twisting, tumbling fuselage slammed into the ground a moment later, scattering debris for more than 1,500 feet along a shallow gully before the wreckage came to rest in the freshly fallen snow.

Fuselage Breaks Up

The left wing disintegrated in the initial impact, Burnett said. The fuselage then broke into three pieces--the tail section; the center section, which overturned completely, and the forward section, which landed on its side. The passengers and crew were all in the forward and center sections.

The NTSB chief said that a United Air Lines pilot landing on a parallel runway reported “a big fireball” in the seconds after the crash, but there was relatively little damage or injury because of the fire.

Investigators were hurrying Tuesday to collect evidence at the crash site before the onset of another snowstorm, expected to hit the Denver area before dawn today.

Burnett said that once the crash site field work is completed, the wreckage can be moved--perhaps to an airport hangar--for further examination.

That would permit the reopening of Runway 35 Left--one of the airport’s two north-south takeoff strips--which has been closed since the crash Sunday afternoon.

Builder Issued Warning

Burnett said Tuesday that after three non-fatal accidents showed the DC-9 Model 10’s “sensitivity to icing on the upper surface of the wing,” the manufacturer issued a warning bulletin.

In addition, he said, the NTSB technical staff prepared an internal memo on the subject, although this memo was never delivered to the board or acted upon. The memo stated that aircraft without slats “are sensitive to even light amounts of airfoil ice, which may not always be detectable and which may accumulate during pre-takeoff taxi operations.”

The Model 10 accidents cited by the NTSB included the crash on takeoff of an Ozark Airlines jetliner in Sioux City, Iowa, on Dec. 27, 1968, the crash landing of a Trans World Airlines passenger plane while taking off from Newark, N.J., on Nov. 27, 1978, and an aborted takeoff by an Airborne Express freightliner in Philadelphia on Feb. 5, 1985.

Burnett said that a transcript from the plane’s “black box” cockpit voice recorder--recovered from the wreckage after the crash--may provide the answer. The tape from the recorder is being studied in Washington, D.C., and results are expected later this week.

A few miles from the airport, about 400 mourners on Tuesday filed into a chapel at the Denver University for Continental’s memorial service honoring the victims of Flight 1713.

A handful of pilots in their crisp blue uniforms nodded solemn greetings to each other across the pews of Whatley Chapel. Two uniformed police officers in the congregation joined hands, heads bowed, for the blessing. Another police officer identified them as the precinct captain and an officer who had been on duty at the crash site.

‘Bind Broken Hearts’

The Rev. Gilbert Horn, executive director of the Colorado Council of Churches, opened the service by urging mourners not to look for someone to blame in the tragedy, but to use this as “a time to knit a circle of grief and to bind broken hearts.”

After a Roman Catholic priest and a Jewish rabbi offered prayers, Continental Chairman Frank Lorenzo stepped forward from a front pew to address the mourners.

“We grieve for the relatives, friends and employees who have been affected by this very unfortunate accident,” Lorenzo said. “We also ought to wish the very best for a very speedy recovery for the men and women that are still injured . . . some quite seriously.”

Lorenzo also expressed gratitude to the city’s emergency workers and hospital personnel, saying that while Denver “obviously has been touched by an enormous amount of tragedy and sorrow (it) also has been touched by a great amount of heroism.”

Colleagues and friends of the three dead crew members filled the foyer after the brief service, clinging to each other in tearful, wordless embraces.

Staff writer Tamara Jones also contributed to this story.