Incident Partenavia P.68B Victor VH-IYM,
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ASN Wikibase Occurrence # 206663
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Date:Thursday 2 January 1992
Type:Silhouette image of generic P68 model; specific model in this crash may look slightly different    
Partenavia P.68B Victor
Registration: VH-IYM
MSN: 143
Year of manufacture:1978
Fatalities:Fatalities: 0 / Occupants: 2
Aircraft damage: Substantial
Location:Moorabbin Airport (YMMB), Moorabbin, VIC -   Australia
Phase: Landing
Departure airport:YMMB
Destination airport:YMMB
Investigating agency: BASI
Confidence Rating: Accident investigation report completed and information captured
The private pilot conducted a daily inspection, loaded five people and luggage on board the aircraft and attempted a takeoff on runway 17 right. When the aircraft failed to rotate, the pilot rejected the takeoff. He attempted a second takeoff on runway 17 right, using the extra runway distance available before the displaced threshold. Again the aircraft failed to rotate and the takeoff was rejected. He taxied back to dispersal, unloaded 75 kilograms of luggage and attempted a third unsuccessful takeoff. Next he unloaded the four passengers and attempted a fourth takeoff which was also rejected. The pilot taxied back to dispersal and acquired the services of a flying instructor in an attempt to determine why the aircraft would not rotate when he pulled the control column back. The instructor agreed to fly a circuit with the pilot. The pilot carried out a takeoff with the instructor monitoring. Because the instructor was not flying the aircraft he was not aware that the pilot had to apply stabilator back trim to rotate the aircraft. During the crosswind leg the instructor noted that the pilot was holding an unusual control column position to achieve the climb attitude.

The instructor took over the controls but realised that, although the control column pressures felt normal and ailerons performed normally, there was little or no attitude change when the column was pushed forward or pulled aft. Using engine power variations and stabilator trim, the instructor carried out a long, shallow, landing approach for runway 17 right. The instructor was unable to reduce the rate of descent enough to prevent a hard landing. On touchdown the right main landing gear leg broke and the aircraft skidded off the runway to the left. It was subsequently found that stabilator control was lost because the torque tube lever (drive horn) slipped on the stabilator torque tube. There was evidence of lubricant between the clamping surfaces of the drive horn and the stabilator torque tube. Lubricant had been applied to the area during recent assembly in an attempt to prevent corrosion which had occurred in the past on an unpainted torque tube. Lubricant may also find its way onto the torque tube/drive horn when the jack screw, which is located immediately above the drive horn, is lubricated.

The rigging screw/safety screw, which located the drive horn on the torque tube, had sheared progressively. It was estimated that this screw will shear with a control force of 60 pounds. A series of tests was carried out to measure the breakaway and sliding forces of the drive horn on the torque tube with the drive horn clamp bolts properly torqued between 50 and 70 inch pounds. These tests were conducted without fitting a rigging screw. With lubricated surfaces, the maximum breakaway force was 96 pounds with the clamping bolts torqued to 70 inch pounds. The breakaway force fell to 45 pounds with clamping bolts torqued to 50 inch pounds. The highest breakaway force measured during the tests was 165 pounds with dry surfaces and 60 inch pounds torque on the clamping bolts. These tests indicated that the current design does not comply with FAR 23.397 standards because the control system is not capable of transmitting a force of 200 pounds to the stabilator without risk of slippage of the drive horn on the torque tube. The rigging/safety screw probably failed as a result of being subjected to repeated shearing forces during flight.

Accident investigation:
Investigating agency: BASI
Report number: 
Status: Investigation completed
Download report: Final report


Revision history:

25-Feb-2018 07:56 Pineapple Added
25-Jan-2020 12:43 Uli Elch Updated [Aircraft type]
25-Jan-2020 12:44 Uli Elch Updated [Aircraft type]

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