Thermal Day at a Controlled Field with a Late Clearance
You are launching by aerotow from a controlled aerodrome with a 1200 m grass runway. ATIS gives QNH 1018, surface wind 220/12 kt, and runway in use 22. Your glider has a maximum take-off mass of 600 kg and a placarded maximum aerotow speed of 130 km/h. The tow pilot briefs 110 km/h for the climb. During the take-off run, the tower clears a landing airliner to touch down on the same runway and instructs you to 'expedite, traffic on short final'. Your tow plane is already at 40 kt and accelerating; you are 300 m from the upwind threshold. The tug continues. You release at 450 m AGL in lift of 1.5 m/s, but the cloud base is 1400 m and the wind is forecast to increase to 25 kt by mid-afternoon with gust spread of 10 kt.
1. Assess whether the 'expedite' instruction changes your take-off decision, and state the actions and communications you would use.
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The instruction is a request to minimise delay, not an authorisation to abandon the take-off performance calculation. Once the tow plane is at 40 kt and committed, an abort would leave you on the runway in front of landing traffic, which is the greater hazard. The correct decision is to continue the aerotow, maintain the briefed 110 km/h climb speed, and clear the runway environment promptly.
Key reasoning: (1) A go/no-go decision must be made before the take-off run begins; after commitment, the abort distance and the traffic behind you make stopping worse than continuing. (2) You cannot outclimb an airliner on short final - separation is achieved by the tower, not by your climb rate. (3) Communicate: acknowledge 'expediting, glider rolling' so the tower knows your state, and after release call 'glider clear of runway, climbing to the west'.
If the situation had been ambiguous before the roll - for example, an unclear clearance or a tug that had not begun its run - the correct answer would be to hold and query. The judgement tested is distinguishing a pre-commitment decision from a post-commitment one.
2. Given the forecast wind increase and gust spread, evaluate the wisdom of continuing the flight and describe your decision points.
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The forecast of 25 kt mean wind with a 10 kt gust spread by mid-afternoon, on a day with 1400 m cloud base and 1.5 m/s thermals, points to increasing mechanical turbulence and a rougher, lower-quality thermal field. On a 1200 m grass strip aligned 22, a 25 kt wind at 220° is nearly down the runway, so crosswind is not the limiting factor; the limiting factors are gust-induced turbulence near the surface and the reduced margin for a safe outlanding.
Decision points to set before continuing:
- A hard turnaround time based on the forecast, not on how good the lift feels.
- A minimum working height (for example 600 m AGL) below which you head for the field rather than search for lift.
- A check of the actual surface wind and gust spread on the next ATIS or by asking the tower before you commit to returning.
- A pre-selected alternate off-field landing area within gliding range, chosen with the wind direction in mind.
Continuing is defensible only if you keep a generous height margin and a firm return time. If the surface gust spread reaches the point where you cannot reliably control the approach, the correct action is to land early rather than to stretch the flight.