Pilot flies into freezing rain

This December 2008 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

Aircraft: Piper Cherokee Six. Injuries: 1 Fatal. Location: North Canton, Ohio. Aircraft damage: Destroyed.

What reportedly happened: The pilot, who had logged 510 hours, obtained a weather briefing prior to departure on the night flight in instrument conditions. During the briefing, he stated he planned to fly the route at an altitude of 6,000 feet. He learned that the freezing level was about 3,000 to 4,000 feet, and that it was likely that it would drop to the surface as the day progressed. He indicated he was aware of the hazardous weather conditions and expressed concern about them.

The pilot took off. Meteorological analysis showed a high likelihood of encountering supercooled large droplet icing in the area. General aviation pilots operating into and out of the airport around the time of the accident all reported icing conditions, with rapid accumulations in freezing rain with most of the icing occurring between 3,000 to 3,500 feet. One pilot reported that he required a significant amount of engine power to maintain airspeed and had a hard landing due to ice accumulation on his airplane.

As the accident airplane approached the airport, the local air traffic controller issued the pilot a vector to the ILS course about two miles from the runway’s ILS outer marker. The controller advised the pilot to maintain 3,200 feet until established on the approach, and that the airplane was cleared for the approach. The pilot acknowledged the clearance and asked if there were any pilot reports of icing below 6,000 feet in the area. The controller responded that there were no reports of icing at that time, but asked the pilot to advise if he encountered any.

The pilot made a gradual left turn to intercept the localizer, and then leveled out near the approach course heading. Although left of the localizer course, the pilot began descending on the approach and stabilized the airplane at an airspeed of just over 100 knots. The controller told the pilot that he was left of the approach course. The pilot acknowledged and reported that he was correcting, however, recorded radar track information showed that the pilot did not correct, but continued to fly a course to the left of, and almost parallel to, the approach course centerline.

The controller then told the pilot that he was well left of the approach course. The airplane briefly turned right toward the approach course centerline, but seconds later, the airplane rolled into a 30° left bank, and away from the approach course centerline. While at 2,800 feet, the pilot began a nonstandard 360° turn. The airplane was now 2.5 miles northeast of the airport. The pilot stated he was attempting to re-establish the airplane on the approach course. The controller responded that he was unable to approve the pilot’s request, but the pilot was already in the turn.

The controller then instructed the pilot to climb and maintain 3,000 feet. The airplane’s bank gradually increased to about 40°. The controller asked the pilot for his present heading and the pilot responded “due north and climbing.” The airplane began to climb while remaining in a 30° to 40° left bank. The controller instructed the pilot to climb without delay. The airplane’s pitch increased while the airspeed significantly decreased. Shortly thereafter, the airplane entered a spiral-like dive and the pilot declared an emergency. The controller advised the pilot to maintain altitude and indicated that the airport was two miles to the west. The pilot did not respond. There was no further contact with the airplane.

A witness on the ground saw the airplane come out of the clouds in a nose-down attitude. The engine sounded as if it was producing full power. The post-accident examination of the airplane revealed no anomalies that would have precluded normal operation.

Analysis of recorded radar data indicates that the airspeed, roll, and initiation of a climb brought the airplane close to an aerodynamic stall as it was maneuvering in a steep turn following the controller’s instruction of “no delay” and the pilot’s declaration of an emergency. The airplane subsequently stalled and rapidly descended to the ground. The characteristics of the descent are consistent with an abrupt stall during maneuvering that was likely aggravated by ice accumulation on the airplane.

Investigators determined the risk factors for spatial disorientation were present at the time of the accident, including dark night instrument meteorological conditions and maneuvering flight. The airplane’s sequence of sustained turns was conducive to spatial disorientation. Furthermore, the pilot’s report that he was headed “due north and climbing” as he placed the airplane into a turn of decreasing radius was inconsistent with his having an accurate awareness of the airplane’s orientation.

The pilot had a history of seasonal allergies, treated with prescription medication that was reported to the FAA. While an over-the-counter sedating antihistamine was found in the pilot’s blood during post-accident toxicology testing, the investigation was unable to determine if the pilot was adversely affected by impairment.

Probable cause: The pilot’s inappropriate control inputs as a result of spatial disorientation, which led to an aerodynamic stall and loss of control. Contributing to the accident were the pilot’s decision to conduct flight into known icing conditions, ice accumulation that reduced the airplane’s aerodynamic performance, and the pilot’s failure to initially intercept and establish the airplane on the proper approach course.

For more information: NTSB.gov