| Occurrence Briefs are concise reports that detail the facts surrounding a transport safety occurrence, as received in the initial notification and any follow-up enquiries. They provide an opportunity to share safety messages in the absence of an investigation. |
What happened
On 12 September 2019, a Diamond DA 40 departed Bankstown, New South Wales (NSW) for a solo navigation training flight with a student pilot on board.
During approach into Dubbo, NSW at about 500 ft AGL, the pilot extended full flap to prepare the aircraft for landing. Once full flap had been extended, the pilot noticed that he was unable to move the control stick to the left and as a result, the aircraft was unable to roll to the left. He immediately retracted the flaps to the take-off position, regained aileron authority and landed without further incident.
Engineering Inspection
Following the incident, the engineering inspection revealed that a spacer under the flap actuator control rod (Figure 1) was incorrectly re-installed above the flap actuator rod during a routine 200-hourly maintenance inspection.
During the inspection, the bolt attaching the idler arm to the actuator control rod was removed to allow for a bonding cable to be repaired. The flap system was inadvertently activated, resulting in the idler arm and the actuator control rod separating. When this was re-assembled, the spacer was incorrectly positioned on top of the actuator control rod. As a result, the bottom of the flap control rod was displaced downwards by the incorrectly placed spacer causing the cam to catch on the underlying aileron control rod when the flap was extended to the fully deflected landing position. Consequently, the control stick was unable to be moved left of the central position when the flaps were fully deflected.
Although a post-maintenance check flight was conducted before the incident flight, the problem was not detected. The manufacturer’s aircraft flight manual does not require a check of the flight controls in the landing position prior to take-off or during the check flight. Company standard operating procedures called for the extension of landing flap once established on final approach, but as the weather conditions were smooth, the flaps were not extended fully and therefore the fault was not detected.
The manufacturer’s post-maintenance check flight checklist also did not require a check of the flight controls with flap fully extended.
Figure 1: Flap actuator installation
Source: Diamond DA 40 Aircraft Maintenance Manual
Safety action
As a result of this incident, the training organisation has advised the ATSB that they have taken the following safety action:
- Pre-flight checklists for all DA 40 flights have been updated to include an item to check that flight controls are full, free and functioning correctly at all flap positions.
Safety message
This incident highlights the importance of maintenance procedures and post-maintenance checks being carried out comprehensively and systematically. While the aircraft is in maintenance, all components must be refitted and reinstalled in accordance with the aircraft’s maintenance manual. Once tasks are completed, it is vital to verify the functionality of all critical aircraft components before returning it to service.
About this report
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.