The following article is based on information contained on the UK Airprox Boards's web-site, (see further reading).
About 10% of all UK Airprox are glider-related – that’s about 20 incidents a year. Almost all occur in Class G airspace which is of course for everyone to use. In such airspace, “see and avoid” is the primary means of collision avoidance. Modern gliders can be very difficult to see so a better understanding of where gliders may be found should assist everyone to choose routes and levels that minimise the chances of an encounter. The UK Airprox Board’s gliding specialist offers the following advice to pilots, drawn from Airprox.
Glider sites are clearly marked on the topographical charts but be careful with some versions - and particularly electronic charts - as not all publishers have included them yet. Note that the heights shown on the charts refer to the maximum height of a winch launch. On CAA charts these are currently shown as the altitude above sea level (QNH). If height above the site (QFE) is used, either on older CAA charts or on a non-CAA chart, then note that most gliding sites specify a maximum winch launch height of either 2000ft or 3000ft above ground level. Several sites are perched on tops of hills so a glider’s altitude (QNH) at the top of a winch launch could be 4000ft if the site is 1000ft above sea level.
Avoiding the winch launch area is essential as the wire will certainly cause structural damage and probably remove a wing with fatal consequences, irrespective of aircraft size. But just avoiding the winch height/altitude by a margin may not be sufficient to avoid a close encounter as several gliders may well be in the area having been launched earlier. The airspace above the winch launch may also be full of gliders. In addition, many of the sites will use aircraft to launch, typically anywhere between 2000ft and 4000ft above the site and occasionally higher.
The best advice is therefore to avoid a glider site by a good margin if at all possible, paying particular attention to the areas immediately above and upwind of the site. Most summer operations can be assumed to be up to cloudbase but can be well above it when wave conditions prevail. Wave can occur at any time but is generally more active during winter months, particularly at those sites that are nearer hill and mountain ranges.
If you find yourself approaching a glider launch site, do not rely on the launch crew seeing you in time to stop a launch. Calculations have shown that if you are flying above 120kts it is unlikely the launch crew will see – or hear - you in sufficient time to take such action.
Finally, gliders can be safely launched in very high wind speeds so it is unwise to assume the site is not launching just because other GA airfields in the area have ceased operations.