DC-9 Stall During Takeoff Due to Undetected Ice Accumulation

Casualties unknown • Philadelphia, PA, US

A DC-9 experienced an uncommanded roll and engine stalls shortly after takeoff due to a thin layer of ice on the wings, which went undetected during pre-flight checks in freezing drizzle.

What happened

Following landing, the aircraft remained parked on the ramp for approximately 39 minutes while cargo was loaded. During this period, light freezing drizzle fell intermittently, mixed with ice pellets and snow. The crew performed visual inspections of the aircraft surfaces from both the cockpit and the entry door but observed no visible ice or snow adhering to the tops of the wings, nose section, windshield, or area above the door. Despite other aircraft undergoing de-icing procedures, the captain declined an offer to de-ice the plane.

The takeoff began normally with an 18-degree nose-up attitude. However, just after lift-off, the aircraft entered an uncommanded left roll, causing both engines to experience compressor stalls. The captain corrected the attitude using left aileron and rudder input and initiated a takeoff abort. The aircraft touched down left of the runway on the tail skid and right wing tip, approximately 5,600 feet from the threshold on a 070-degree heading. It then traveled another 2,025 feet in a sweeping right arc, striking two runway signs before coming to rest with its heading pointing west and the right pylon bent downward.

The investigation

Investigation revealed that a thin layer of ice, estimated at 0.15 inches thick, had accumulated on the wings. This accumulation raised the aircraft's stall speed. When the DC-9-15 stalled, the engines became susceptible to compressor stalls due to the altered airflow conditions.

Findings

The primary causal factor was ice accumulation on the wings, which increased the stall speed and led to engine failure during the critical climb phase. The crew's decision to forgo de-icing based on visual inspection proved insufficient given the precipitation type.

Probable cause

Ice accumulation on the wings that raised the stall speed and caused compressor stalls, resulting from the crew's failure to detect the ice and decline de-icing services.

Frequently asked questions

What happened in the 1985-02-06 Mcdonnell Douglas DC-9-15 accident near Philadelphia, PA?

A DC-9 experienced an uncommanded roll and engine stalls shortly after takeoff due to a thin layer of ice on the wings, which went undetected during pre-flight checks in freezing drizzle.

What aircraft was involved and where did it happen?

The accident on 1985-02-06 involved a Mcdonnell Douglas DC-9-15, registration N926AX, at Philadelphia, PA.

What was the probable cause of the accident?

Ice accumulation on the wings that raised the stall speed and caused compressor stalls, resulting from the crew's failure to detect the ice and decline de-icing services.

Investigation report by the U.S. National Transportation Safety Board (NTSB) historical archive. Original record: https://carol.ntsb.gov/event/20001214X35671. This page is a structured re-presentation; facts and quotes are in the National Transportation Safety Board (NTSB), United States.

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