ANC96FA162

The aircraft (acft) took off from Lake Hood Seaplane Base with 5 occupants aboard. Witnesses said that after lift-off, flaps were retracted & acft pitched to a climb attitude; but stopped climbing & began settling, then struck a utility pole at the airport boundary. It then crashed on a road, & a fire erupted. Calculations showed acft was within allowable weight & balance parameters. Engine exam revealed brass throttle arm (PN 632555-23) was worn & had disconnected from the throttle linkage. It had disconnected where a hard steel bushing (with splines) had been installed (pressed) in a mounting hole in the relatively soft throttle arm. The mounting hole had become 'U' shaped with one side open. The opening was large enough to allow passage of the throttle linkage connecting bolt & bushing. Deposits of material from the throttle arm were found on the bushing splines. The deposits were consistent with rotational motion of the bushing within the mounting hole, as if rotation occurred while tightening the bolt. Teledyne Continental Service Bulletin SB95-2, dated 4/21/95, provided inspection & lubrication procedures for throttle linkages at each 100 hr, progressive, and/or annual inspection. Acft had been flown 80 hrs since its previous (annual) inspection on 8/11/96.

History of flight

On September 23, 1996, at 1700 Alaska daylight time, a float equipped Cessna 206G airplane, N7312C, registered to Stearns Air Alaska of Anchorage, Alaska, crashed during initial climb after takeoff from the Lake Hood Seaplane Base, Anchorage. The on demand air taxi flight, operating under 14 CFR Part 135, was departing Lake Hood for a sightseeing flight to Mt. McKinley. A company visual flight rules flight plan was in effect and visual meteorological conditions prevailed. The certificated commercial pilot and two passengers were fatally injured and two passengers were seriously injured. The airplane was destroyed by post impact fire.

Witnesses

During an interview with the NTSB investigator-in-charge, Anchorage Airport Safety Officer Marty Spinde, stated he watched the airplane takeoff. The takeoff run was normal and the airplane lifted off with, "plenty of room to spare." The airplane began to climb, and the officer stated that when the "pilot cleaned up the airplane" the airplane began to descend. He stated he could see the flaps retract.

According to a witness who watched the entire accident sequence, he stated that the engine was running, "OK", but the airplane's nose had a high angle of attack. The right float struck a high tension power line, flipped inverted, and crashed to the ground on Northern Lights Boulevard.

Another witness, Lt. Tibor of the Anchorage Airport Police, stated the engine was running normally at a high RPM. The airplane acted like it was overloaded and had a high "angle of attack." He saw a float strike the telephone pole wire support, flip upside down and crash onto Northern Lights Boulevard.

Mr. Roland Kenneson witnessed the airplane during the initial climb. He stated the airplane cleared a 60 foot high dirt pile located in the state maintenance yard. He stated the flaps were extended to 20 degrees and he saw the flaps retract to 10 degrees. The airplane then began to settle. He said the engine sounded "doggy" as if the propeller was in the cruise RPM setting. The engine sounded steady and he stated that it sounded like the airplane was heavy with an aft center of gravity. He estimated the highest altitude the airplane reached was approximately 100 feet above the ground, just over the tree tops. The airplane's speed seemed slow. He observed the airplane flying wings level with the nose of the airplane high.

Injuries to persons

The pilot and two passengers were fatally injured and subjected to fire. Two passengers received serious thermal injuries.

Damage to aircraft

The airplane cockpit and cabin were involved in a post impact fire. The engine separated from the engine compartment and was found resting under the root of the right wing. The entire wreckage was resting inverted. One float was damaged by fire and the other float separated and was not damaged. The fire consumed the engine compartment, the instrument panel, cockpit, cabin, and portions of the empennage, part of the right float and associated struts.

Other damage

The airplane struck a cross member on a telephone pole which supported two high tension power lines. One of the power lines was severed.

Personnel information

According to Federal Aviation Administration records and the Company records, the pilot had a total flight time of 5,000 hours. His last application for a medical certificate, dated 2/29/96, shows he had flown 450 hours in the previous six months. A review of the pilot records for the months of August and September show a monthly total flight time of 125.6 hours and 76.7 hours respectively.

The direction of Northern Lights Boulevard aligns with 256/076 degrees. The airplane struck a high tension power line utility pole, which was located on the south side of the road, and struck the road 105 feet past the utility pole on a magnetic bearing of 312 degrees. The float of the airplane struck the upper cross member on the utility pole and severed one power line. The other power line separated from the cross member and sagged down.

The nose of the airplane aligned with 120 degrees. The ditch in which the wreckage came to rest was approximately 4 to 5 feet below the surface of the road.

The calculated height of the utility pole, above the road's surface, was determined to be 53.5 feet. The utility pole was erected off the side of the road in soft terrain that was below the surface of the road.

Flight control continuity was established between the flight control surfaces and the cockpit yoke mechanism. The engine controls were not attached to the engine. The flaps were in the up position but were damaged by fire and impact.

The left float, which separated from the main wreckage and did not burn, had rolled upside down and the sealing balls in the float compartments were missing. The float was rolled right side up and each of the compartments was pumped out. No water was found.

The propeller remained attached to the engine but each of the blades was broken inside the hub assembly.

The fuel injector lines were checked prior to engine removal and all were found to be connected. The throttle cable linkage was found disconnected from the throttle arm at the accident site, although the castellated nut was in place on the end of the bolt which attaches it to the throttle arm. The castellated nut was fastened with a locking cotter pin.

Medical and pathological information

The autopsy report shows that the "anterior descending branch of the left coronary artery had extensive and severe arteriosclerotic change which virtually completely occluded the lumen approximately 0.4 cm from its bifurcation from the circumflex."

A statement submitted by Anne M. Stearns revealed that on September 20, 1996, the pilot had helped her and her husband, the owner of the operation, push back an airplane. The pilot complained the next morning of experiencing severe chest pains and he thought the pains were related to the activities of the previous evening which consisted of pushing back the airplane.

Unspecified levels of drugs, typically associated with over the counter cold medications, were discovered in toxicological samples taken from the pilot. See attached toxicological report.

Tests and research

The engine was removed from the accident and externally examined at Sea Air Inc., under the supervision of the NTSB IIC. The left and right magnetos were removed and bench checked. They checked normally. All had blue and even sparks.

The spider and fuel injector line assembly was removed and flow checked. The flow streams were even/equal and straight. The fuel screens were clean.

The flap jack screw was measured and found to have 1 inch of threads showing. According to Cessna Aircraft Company, this equates to having 5 degrees of flap extended.

The elevator trim screw was located and it showed 1.5 inches of threads. Cessna Aircraft stated that this equates to a neutral trim position.

The rest of the engine was shipped to Teledyne Continental Motors in Mobile, Alabama. The engine was disassembled under the supervision of the NTSB IIC, and no mechanical anomalies with the engine, other than the throttle arm, were discovered.

The throttle arm assembly connected to the throttle plate was removed and examined by a metallurgist at Continental. The brass arm, Continantal part number 632555-23, had a section of metal missing from around the throttle cable mounting hole. The missing metal was sufficiently large enough to allow the passage of the throttle cable linkage attachment bolt. The brass around the hole in the throttle arm was necked down and was thinner than the main brass section of the throttle arm. The steel bushing remained attached to the throttle cable and the steel bushing would not spin on the mounting assembly. According to a representative of Teledyne Continental Motors (TCM), if the throttle cable li