Incident Overview
On 3 October 2013, Sea King Mk 4 ZE428, operated by 845 Naval Air Squadron based at Royal Naval Air Station Yeovilton, was conducting a composite training sortie that included abseiling and a 40ft Advanced Single Engine Failure (ASEF) exercise. The aircraft captain was a Qualified Helicopter Instructor (QHI) graded as an A2 QHI, while the handling pilot (HP) was a pilot pending award of a Certificate of Competence (CofC). An aircrewman was stationed in the cabin, and another pre-CofC pilot was seated in the cabin awaiting his turn for an abseil exercise.
Sequence of Events
After completing an abseiling exercise, the aircraft repositioned to the threshold of Runway 04 for the 40ft ASEF exercise. The QHI briefed the exercise and conducted a demonstration landing, which caused the cabin door Helicopter Emergency Egress Lighting System (HEELS) to illuminate and generated three Health and Usage Monitoring System (HUMS) exceedances. The QHI did not consider these unusual for the exercise. Due to the firm landing, the QHI decided to start the HP's exercise from approximately 30ft with a slightly higher manual engine power setting.
The HP initiated the exercise by selecting a nose-down attitude and then correcting with aft cyclic. As the aircraft reached 4 degrees nose-up, the tail wheel struck the ground and detached, coming to rest about 10 meters from the impact point. The aircraft then pitched forward onto the nose and then back onto the rear lower fuselage near the tail wheel mounting, causing damage to the airframe. The aircraft came to an upright stop on the taxiway. The crew shut down the engines, called for assistance, and egressed without further incident. The aircraft was subsequently declared as Cat 3 Depth.
Crew Background
The QHI had 3,136.25 total flying hours, with 1,715.20 on the Sea King Mk 4, and had been an instructor since November 2008. He served as the squadron's Principal Training Officer (TO1). The HP had 564.40 total flying hours, 386.20 on the Sea King Mk 4, and had flown 49.45 hours in the three months preceding the incident. He had not yet completed the CofC requirements due to outstanding exercises including the abseil and 40ft ASEF. The aircrewman had more than 460 hours of experience but had not previously participated in a 40ft ASEF exercise.
Aircraft Information
Sea King Mk 4 ZE428 entered service on 17 December 1985 and had accumulated 9,247.35 airframe hours. It had been modified to the Theatre Entry Standard (TES). The aircraft was serviceable at the start of the sortie, having undergone a Partial Test Flight earlier that day to confirm replacement of the Radar Altimeter. The basic weight on the day of the incident was 16,850 lbs. For the sortie, the fuel load was 3,600 lbs, resulting in an all-up weight of approximately 19,950 lbs on takeoff.
Sortie Preparation
The sortie was initiated by the HP to complete abseiling exercises required for nine squadron pilots. The HP coordinated with the QHI and the Commando Mobile Air Operations Team (Cdo MAOT) to ensure availability of abseilers and an instructor. Six pilots were scheduled to fly under the QHI's supervision, including five pre-CofC pilots and one on a refresher course. The HP requested to add the 40ft ASEF exercise to the sortie, as these two exercises were the only remaining items in his CofC task book. The QHI agreed, and the HP was scheduled to be the first to fly the abseil serial before the ASEF exercise.
The abseiling portion was thoroughly briefed, but the 40ft ASEF was mentioned only briefly; the QHI planned to brief its details in the aircraft before the exercise. The sortie was out-briefed and authorised by the squadron senior pilot in accordance with Commando Helicopter Force (CHF) Flying Order Book procedures.
Timeline
The sortie departed dispersal at 12:24 local time. The incident occurred approximately 4.5 hours into the crew's duty day, near the beginning of the sortie. The QHI reported 8 hours of sleep before the shift, rating his alertness as 'ideal'. The HP also had 8 hours of sleep and rated his alertness as 'okay'. Both were deemed fit to fly. The HP had scheduled a medical examination for the afternoon and attended the medical centre between the morning brief and the sortie brief.