Cessna 182 accident at Minnesota, 8 Nov 1972 (N70586)

Accident narrative

At approximately 1029 central standard time on November 8, 1972, a Cessna 182, registration N70586, crashed in a wooded area while executing a precision radar approach to Runway 9 at Duluth International Airport in Minnesota. The aircraft was destroyed by impact forces and a post-impact fire. The two passengers were killed, and the pilot was seriously injured.

### The flight

The general aviation business flight was transporting two University of Minnesota employees from St. Paul to Duluth. The pilot, who held a commercial certificate, had accumulated approximately 767 flying hours, all of which were in the Cessna 182.

Before departing St. Paul at 0855, the pilot received a weather briefing from the Minneapolis Flight Service Station. The briefing included a Duluth forecast for low ceilings and visibilities, as well as an area forecast for light to occasional moderate mixed icing in clouds and precipitation above the freezing level. The flight proceeded under instrument flight rules, initially at 9,000 feet before being cleared to 6,000 feet near Duluth.

### The sequence of events

At 0935, the pilot requested the Duluth weather. Approach Control reported a measured ceiling of 300 feet and a half-mile visibility with fog. The controller did not relay two other recent pilot reports: a Piper Aztec pilot's report of picking up heavy ice during a missed approach 20 minutes earlier, and an Air Force T-33 pilot's report that the ceiling was between 150 and 200 feet.

N70586 was cleared for an Instrument Landing System (ILS) approach to Runway 9. At 1012, the pilot advised the tower he was executing a missed approach. He reported trouble with his gyrocompass and requested a Precision Approach Radar (PAR) approach using a "no gyro" procedure, in which the controller instructs the pilot when to start and stop turns. The flight was cleared to 3,000 feet to return for another approach.

During a procedure turn at 1021, the pilot advised, "I was just picking up some ice, if I miss it this time I'll have to climb out." The PAR controller stated that the aircraft intercepted the final approach at a very high angle and fell below the glidepath. About two miles from touchdown, the pilot stated he was picking up ice and began a rapid left turn. The controller instructed him to turn right and asked if he wanted to continue the approach; the pilot replied "Yes." The left turn continued, and the aircraft fell further below the glidepath.

The pilot later stated that ice continued to build during the approach and he experienced increasing difficulty holding altitude. He was unable to maintain altitude even with full power. At 1025, the pilot acknowledged missed approach instructions. This was the final transmission from the aircraft. It crashed approximately 2-1/4 miles from the runway threshold.

### What the investigation found

Wreckage examination revealed no separation of structural components prior to impact. Most of the fuselage and inboard wings were subjected to intense ground fire. The propeller blades showed considerable torsional twisting. The aircraft was equipped with a heated Pitot tube and a windshield defroster, but had no other deicing or anti-icing equipment. The gyrocompass was too heavily damaged by fire to provide meaningful information, but the Board noted the aircraft was equipped with sufficient other instruments for an instrument-rated pilot to conduct a safe flight without it.

The Board noted that while the controller had an opportunity to provide the pilot with the Aztec's icing report and the T-33's lower ceiling report, there was overriding evidence of the pilot's determination to land. The Board observed that the pilot was aware of forecast icing before departure, and that any doubt about the actual weather should have been dispelled during his first approach. Despite airframe ice and marginal weather, he decided to attempt a second approach.

The Board concluded that ice accretion eventually affected the airframe surfaces to the point that the aircraft could no longer remain airborne even with full power, leading to a loss of control.

### Probable cause

The National Transportation Safety Board determined that the probable cause of the accident was "the action of the pilot in continuing operation in known icing conditions without aircraft deicing or anti-icing equipment, which resulted in a loss of control because of ice accretion on airframe surfaces."