ASN Wikibase Occurrence # 238195
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| Date: | Friday 17 July 2020 |
| Time: | |
| Type: |  Schleicher ASK 21B |
| Owner/operator: | Kennemer Zweefvlieg Club |
| Registration: | PH-1637 |
| MSN: | 21976 |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Terlet Airfield, Gelderland -
 Netherlands
|
| Phase: | Landing |
| Nature: | Private |
| Departure airport: | Terlet Airfield (EHTL) |
| Terlet Airfield (EHTL) | |
| Investigating agency: | Dutch Safety Board |
| Confidence Rating: |  Accident investigation report completed and information captured |
The ASK 21 B, a dual-seat glider, took off from runway 22L by means of the winch launch method. There was practically no wind. On board were an instructor and a trainee. The trainee was piloting the glider. Following a short flight, he joined the left-hand circuit at a slightly lower than standard altitude. In his statement, the instructor declared that on the base leg, the airbrakes had been partially opened, a fact confirmed by the available flight data.3 During the final approach, on the instructions of the instructor, the trainee fully opened the airbrakes. This did not result in the desired angle of descent. As a consequence, the instructor then took over control and at an estimated altitude of approx. 30-50 metres, initiated a sharp slip manoeuvre to the left, with full rudder, the aim of which was to lose additional altitude. During this slip manoeuvre, the nose of the aircraft was pointed downwards, and in the course of the manoeuvre, this downward angle increased. The instructor returned the aircraft to a more or less horizontal position just a few metres above the ground, before making a hard landing in the heather, just in front of the airfield landing area. The aircraft bounced up and landed on its nose, left wing down. The glider continued rolling and rotated through approx. 90 degrees to the left, before coming to a stop on the intended landing area. Following the incident, the instructor suffered a painful right arm and shoulder while the trainee remained unharmed. The tail of the aircraft had broken off, the fuselage was twisted and the nose dented.
The aircraft manufacturer declared that during slip manoeuvres, the ASK 21 B, which had been in use by the glider club in question for around two months, did not differ in terms of flying characteristics from the ASK 21. The instructor had a total of over 600 hours of glider experience (3004 launches), over 350 hours of which were in the ASK 21 (over 1900 launches). On the day of the accident, the instructor had completed five instruction take-offs in the aircraft in question. He declared that it had been at least 8 years since he had last landed on runway 22L. The trainee had completed a total of 22 flights.
The flight data showed that the downwind leg was not flown entirely parallel to the winch path. As a consequence, the circuit flown was somewhat tighter, resulting in a shorter base leg, leaving less time to lose altitude. When the aircraft found itself in final approach, where the terrain in front of the landing area slopes downwards, there was almost no headwind, which resulted in an insufficient angle of descent. Partly because the landing runway is relatively short, the instructor felt it was necessary to carry out a slip manoeuvre. In part, this may have been due to optical illusions caused by the relatively wide landing strip, in combination with the downward sloping terrain ahead of the landing area.
Available film recordings of the final approach of the aircraft show that the slip manoeuvre was initiated at low altitude with full rudder extension. This resulted in a high angle and high speed of descent. Notable was the low pitch attitude during the entire manoeuvre. The slip was halted at low altitude, with a level pitch attitude; this left insufficient altitude to slow the high speed of descent and subsequently to land. This resulted in a hard landing.
To carry out a slip manoeuvre with the required precision, it is always important to initiate the manoeuvre gently, and simultaneously keep the nose of the glider above the horizon. It is also vital to have an active awareness of the speed of descent; this should be kept proportional to the flying altitude. At low altitude, the speed of descent should also be low. The manoeuvre should also be terminated gently, at sufficient altitude, at which point the pitch attitude can be lowered, in order to maintain sufficient airspeed.
Sources:
https://www.omroepgelderland.nl/nieuws/2457649/Zweefvliegtuig-crasht-op-vliegveld-Terlet
https://www.kzc.nl/index.php?id=vloot
Media:
#Arnhem 17-7-20 15:20 - Bij Zweefvliegcentrum #Terlet aan de #Apeldoornseweg, is vanmiddag een #Zweefvlietuigje neergestort. De inzittende van het vliegtuigje, zijn er zonder letsel van afgekomen meld de politie. Het vliegtuigje liep wel schade op. pic.twitter.com/wOyHn4Hsnr
— Rick schut fotografie (@RickSchutfoto) July 17, 2020
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 17-Jul-2020 14:24 | RobertMB | Added |
| 17-Jul-2020 16:40 | harro | Updated [Narrative] |
| 17-Jul-2020 16:42 | harro | Updated [Aircraft type, Registration, Operator, Source, Embed code] |
| 17-Jul-2020 16:46 | harro | Updated [Cn, Embed code] |
| 02-Oct-2021 07:12 | harro | Updated [Narrative] |
| 12-Jun-2022 06:15 | Ron Averes | Updated [Location] |
| 29-Sep-2023 07:36 | Ron Averes | Updated [[Location]] |
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