History of the Flight
The aircraft, a Piper PA-28-181 Cherokee Archer (G-LACD), was conducting a training flight with a student pilot and an instructor. The student was practicing glide approaches to a full-stop landing on Runway 09 Left at Barton Aerodrome. The surface wind was reported from 170° at 7 kt, and the grass runway was 518 m in length and wet from recent rain. G-LACD was initially behind another aircraft in the circuit; the leading aircraft extended its downwind leg to allow the crew of G-LACD to fly their glide approach.
During finals, the student deployed full flap but commented that the aircraft was too high. The instructor suggested using a sideslip to increase the descent rate, a technique the student had practiced before. Despite this, the aircraft remained higher than normal when crossing the runway threshold and appeared faster than usual to personnel in the visual control room. The student continued with the landing and initiated a flare, but the aircraft had not touched down by the time it was about halfway down the runway.
The instructor considered ordering a go-around but thought the aircraft might not clear trees and buildings in the climb-out path. His thoughts were influenced by knowledge that this particular aircraft tended to have a slight lag in engine response when selecting full power from idle, which he attributed to an over-rich mixture setting. He therefore decided to allow the student to continue and then brake hard.
After touchdown, both pilots applied hard braking. The aircraft was heading toward the boundary hedge, so the instructor turned right. He felt the wheels lock up. The left wing struck the hedge, causing the aircraft to yaw left and come to rest with the nose in the hedge. The aerodrome fire service was alerted and attended. Both occupants were uninjured and vacated the aircraft normally. Damage was limited to the left wing leading edge and tip.
Aircraft Performance
Performance calculations based on the reported configuration, weight, and zero headwind component indicated that on a paved, dry runway with a full-stall touchdown and maximum braking, the ground roll would have been 256 m. A grass runway increases this distance by about 20%, and wet grass increases it by 30% or, for short grass, by up to 60%. Thus, the actual landing roll would have been between approximately 330 and 410 m, depending on grass length.
Discussion
The accident resulted from an unstabilised approach that appears to have been outside normal parameters and the lack of timely intervention by the instructor to initiate a go-around. The aircraft was evidently high from a relatively early stage of the approach. The leading aircraft's extension of its downwind leg may have influenced the instructor's desire to be expeditious, but it is not clear why the instructor did not order a go-around earlier. He would have been expected to appreciate the aircraft's landing performance and the increased ground roll on wet grass, as well as the lack of headwind or possible slight tailwind. The decision to take control from a student or order an alternative course is not easy, but safety margins should not be compromised for training value.