Introduction
On the morning of 26 October 2024, the pilot of a De Havilland Aircraft of Canada DHC‑2, registered VH‑OHU, departed Hamilton Island aerodrome, Queensland, with 4 passengers on board for a short scenic flight to Whitehaven Beach, Whitsunday Island. Upon touching down on the water, the aircraft yawed to the right, nosed over, and became submerged inverted. The pilot and 4 passengers sustained minor injuries, and the aircraft was substantially damaged.
Right Main Landing Gear Failed to Retract
Immediately following the accident, the right main gear could be seen extended from the float. Examination of the aircraft found no evidence of leakage, loss, or contamination of the hydraulic fluid, and all landing gear circuit breakers were engaged. The nose and left main gear had successfully retracted, indicating the anomaly was likely isolated to the right main gear. During retraction, the main gear travels aft as it swings up into the float. Had the gear been mid-travel, such as still cycling, the impact with the water would have forced the gear to retract up into the float. Therefore, it was unlikely the right main gear moved during the impact sequence.
Post-accident examination identified that the right carriage assembly had seized on the slide tube at the almost fully extended position. Once removed from the aircraft, forceful removal of the carriage revealed advanced corrosion on the right slide tube. The two bands of corrosion were coincident with the location of the carriage bushings, near the full gear extension position. This would be expected as the aircraft was predominantly parked on land, with the gear extended.
The investigation considered scenarios conducive to the formation of this corrosion. The maintenance records prior to the aircraft entering Australia in 2015 were not available, so the service history of the main gear carriage assemblies, including the bushings, was unknown. While there was a significant difference in the condition of the left and right slide tubes, both tubes were installed at the same time and therefore subject to the same operational and environmental conditions. The operator advised the aircraft was rinsed with fresh water at the end of the operating day; however, this was not formally recorded, and there was no practice for rinsing when the aircraft was not operated for several days.
The aircraft records showed the maintainer conducted a 25-hour float inspection on 5 October 2024, and grease was observed on the assemblies during post‑accident examination. However, as there was no requirement to retract the gear for this inspection, the position of the carriage assembly precluded visual examination of the slide tube at the location where the corrosion had developed. Examination of the carriage bushings identified that the right bushings exhibited more wear and loss of the PTFE sliding layer, which runs along the slide tube. This had the potential for galvanic corrosion to form, but required the degradation of the anodised layer on the slide tube to also be present. Insufficient cleaning, inadequate application of grease, and/or accumulation of dust or dirt on the slide tube are known contributors to degradation of protective layers. While the extent to which they were contributory in this case was not able to be determined, it was likely that the identified corrosion resulted in the right main gear seizing.
Pilot Did Not Identify Extended Right Main Gear
The pilot reported observing four blue 'gear up' lamps illuminated, at about Tongue Point and during their pre-landing checks. Passenger footage showed sun glare was not angled in the direction of the landing gear panel, and the pilot advised they were able to clearly identify what lamps were illuminated. However, when tested post‑accident, one blue lamp did not illuminate, although it could not be determined if this failure was due to seawater immersion or pre-existing. Further, the location of the failed lamp could not be determined as the lamps were not identified on removal from the landing gear panel. Despite this, failure of any lamp to illuminate requires troubleshooting by the pilot prior to landing. The pilot can readily determine if the lack of illumination of a lamp is due to a failed bulb or other system issue. The main right gear UP and DOWN proximity switches tested serviceable during the post-accident examination. The examination also noted the right main gear had unlatched from the DOWN location and moved about 1.5–2 mm in the retract direction.
Conclusion
The accident resulted in minor injuries to all five occupants and substantial damage to the aircraft. The investigation identified that the right main gear failed to retract due to corrosion on the slide tube, and the pilot did not identify the extended gear before landing.