Synopsis
On 30 October 2007, a Cessna F172M Skyhawk (registration G-BEMB) experienced an aileron control restriction while on a private flight from Goodwood to Lydd. The pilot, who held a Private Pilot's Licence and had 385 hours total flying experience (290 on type), was accompanied by one passenger. There were no injuries and no damage to the aircraft.
History of the Flight
Shortly after reporting to Shoreham Approach that he was south of Shoreham at 3,100 feet, the pilot encountered a problem with the ailerons. He described the controls as 'freezing' and 'trying to fight back'. To maintain control, he applied increasing right rudder and considerable pressure on the yoke to prevent it from moving to the left. Initially, he suspected a loose object was partially jamming the controls.
The pilot informed Shoreham Approach of the issue. The controller suggested a descent and a right base join for Runway 02. However, the pilot, not wanting to fly over Shoreham town, declared a 'MAYDAY' and reported severe control problems, stating he was unable to land on Runway 02. The controller then cleared him for an approach to Runway 20, which required a downwind landing. The aircraft made an uneventful landing. During taxi to the parking area, the pilot noticed that when he relaxed his grip on the yoke, it moved fully to the left. After engine shutdown and electrical power was turned off, the ailerons functioned normally.
Engineering Investigation
Two days after the incident, an engineering organisation at Shoreham inspected the aircraft. An engineer performed a functional check of the controls, which operated satisfactorily. The aircraft was equipped with a basic autopilot featuring wing levelling and heading functions, activated by two separate rocker switches. The engineer engaged the wing levelling function and reproduced the symptoms the pilot had experienced on the ground. Unable to verify the integrity of the autopilot, the engineer pulled and gagged the autopilot circuit breaker. The aircraft has since flown satisfactorily with the system inhibited.
Comment
The pilot’s and engineer’s reports indicate that at some point during the flight, the autopilot wing levelling function became engaged. The engineer informed the AAIB that, unless there is a fault, the autopilot de-latches when power is turned off and is turned on by moving the rocker switches after electrical power is applied. The pilot stated that he visually checked the autopilot was switched off during his pre-flight check and that neither he nor his passenger touched the autopilot controls during the flight.