Incident Details
On 15 April 2022 at 0545Z, a Cessna 402 aircraft (registration ZS-WRI) departed from Runway 07 at Lanseria International Airport (FALA) on a charter flight to Alldays Aerodrome (FAAL) in Limpopo province. The flight was conducted under visual flight rules (VFR) by day, in accordance with Part 135 of the Civil Aviation Regulations (CAR) 2011. The pilot reported that the pre-flight inspection was normal, and the aircraft carried 1200 pounds of fuel for the planned 35-minute flight.
After take-off, the pilot retracted the landing gear lever, but the red 'gear unlocked indication' light remained illuminated on the instrument panel. Simultaneously, the aircraft yawed to the left. The pilot entered the left-side circuit and leaned the left engine mixture, which restored left engine power. He then yawed the aircraft left and right twice as per the Pilot's Operating Handbook (POH) emergency procedure to obtain three green gear-down indication lights. The pilot contacted FALA air traffic control (ATC) for a visual confirmation of the landing gear position during a fly-past at circuit altitude. The ATC tower reported that the landing gear appeared to be down. The pilot subsequently landed on Runway 07 at 0558Z and taxied to the apron. No injuries were reported, and the aircraft sustained no damage.
Aircraft and Crew Information
The pilot held a valid Commercial Pilot Licence (Aeroplane), initially issued on 10 April 2019, with a Cessna 402 type endorsement, and a Class 1 medical certificate without restrictions, expiring 31 August 2022. The pilot had 936 total flying hours, with 370 hours on type. The aircraft had a Certificate of Airworthiness issued 25 May 2018 (expiry 31 May 2022) and a Certificate of Registration issued 10 October 2014. The 50-hour mandatory periodic inspection was completed on 18 March 2022 at 1498.0 airframe hours, with a Certificate of Release to Service valid until 17 August 2023 or 1598.0 hours. The operator held an aircraft operating certificate (AOC) issued 27 September 2021 (expiry 30 September 2022).
Post-Flight Inspection
A post-flight inspection of the left main landing gear wheel well revealed that a rubber seal on the nut connecting to the left gear hydraulic loaner pump actuator was well-worn. This allowed hydraulic fluid to leak (squirt) when under pressure. The left air filter was removed, cleaned, and refitted; the failed hydraulic hose seal was replaced; the engine bay was washed; and hydraulic levels were topped up. A subsequent test flight confirmed satisfactory operation.
Probable Cause
The probable cause was identified as a failed hydraulic fluid hose seal on the loaner pump, which led to an 'unlocked gear indication' light illuminating at take-off.