LAX96FA317

At flight level 240, the pilot noticed that the wing deice boots were fully inflated, though he had not activated the boots. He consulted the pilot operator handbook, but was unable to cycle the boots. During descent about 5,000 feet msl, there was a loud bang along with a jolt. The pilot noticed that the right wing had imploded or caved in. He also noted that aileron control had been affected. He declared an emergency, was vectored to the nearest airport, and landed without further incident. Postaccident examination of the aircraft revealed: the engine bleed air control valve overboard lines were both plugged with mud about 18 inches up inside from the overboard opening; and both NACA underwing fuel vents were found plugged with mud about 36 inches from the underwing opening. The mud was from wasp nests. There were secondary fuel vents in the fuel filler caps. The right fuel cap vent was 50 percent restricted from a recent wing repaint. Both fuel cap flutter valves were defective. The aircraft had been parked outside for 30 days.

History of flight

On August 24, 1996, about 1050 hours mountain standard time, a Cessna 441, N832AD, received substantial damage to the right wing during descent into Phoenix, Arizona. Neither the pilot nor the pilot rated passenger were injured. Visual meteorological conditions prevailed for the personal cross-country flight and an instrument flight plan was filed. The flight originated at Ozark, Missouri, and was destined for Chandler, Arizona.

While en route at flight level 240, the pilot noticed that the wing deice boots were inflated. They had not been in icing conditions and none was forecast for the route of flight. A review of the pilot operator handbook failed to provide a solution to the inflated boots.

While descending near their destination at 5,000 feet msl, the pilot heard a loud bang and felt the airplane jolt. He observed the right wing to be imploded or caved in. At that time he realized that the aileron control was limited. An emergency was declared and an uneventful landing was made at Phoenix Sky Harbor International Airport.

Postaccident examination of the aircraft revealed: the engine bleed air control valve overboard lines were both plugged with mud about 18 inches up inside from the overboard openings; and both of the NACA underwing fuel vents were found plugged with mud about 36 inches from the underwing openings. The right wing was structurally damaged with similar internal damage to the left wing. There were three right wing rib stiffeners found to have punctured the lower wing skin of the wet wing.

Aircraft information

Prior to the accident flight the aircraft had been parked outside for 30 days at Ozark. The pilot installed the pitot tube covers and the engine inlet covers. He had also stuffed rags in the tail cone area openings to keep birds from nesting in the tail area. There are no protective covers provided for the NACA under wing fuel vents, nor the engine bleed air overboard lines.

According to the aircraft owner, the aircraft had been partially repainted to de-identify it from a Mexican registry during the sale to him. The Mexican registry identification would have been found on the right wing top side and the left wing bottom side.

Testing and research

The fuel filler caps from both wings were sent to the manufacturer for examination and testing. According to the test results, the right wing filler cap secondary vent was reduced by 50 percent due to a paint restriction to the vent holes. The left wing filler cap performed to manufacturer's specification, though some in-service damage was noted. Both fuel cap secondary vent flutter valves failed to meet test specifications due to leakage.

Samples of the foreign material found in both the fuel vent and the bleed air systems were sent to a local college department of entomology for analysis. The material was found to be a product of mud dauber wasps. The mud dauber nestings had some larva present.

Additional information

According to the Cessna Aircraft Company's model 441 maintenance manual, the fuel fillers/caps are to be inspected for damage or damaged components every 200 hours or 12 months, whichever occurs first. There was no detailed inspection information for the fuel cap found in the maintenance data. Also, there was no information found addressing the vent holes or their sizes, or tests, for the flutter valves.