The Quarry That Leans Into the Ring

The error to avoid is measuring the rule from where you stand. The 5.5 km (3 nm) ring is measured horizontally from the aerodrome reference point and applies to where the aircraft is at each instant, not to the launch point.

• Gate at 5.9 km: outside.
• North-west corner at 5.2 km: about 300 m inside.

So roughly one fifth of the polygon sits in airspace where you need approval, even though your launch site is legally clear. Flying the full polygon 'because we take off outside the ring' would be an infringement.

Options, in order of practicality:

1. Re-plan the coverage. Fly only the portion beyond 5.5 km and treat the inner corner as a separate job from a launch point that keeps the whole path outside the ring.
2. Seek approval for the inner portion, with a brief that gives the area, maximum height, times, RPA type and mass, contact numbers, lost-link behaviour, and how you will stay clear of the approach and departure paths. Approval is a conversation, not a formality - expect conditions.
3. Rely on tower hours being closed only after confirming the aerodrome's actual status; do not assume a quiet frequency means the requirement has evaporated.

Separately, the helipad at 500 m is not caught by the 5.5 km rule, but it is a live H24 helicopter operating area. Treat it as traffic: monitor, broadcast if able, and keep the aircraft low and well west of the pad.

The 120 m limit is above the ground directly beneath the aircraft, and 'ground' includes what is built on it.

• Pit floor to pile top: 25 m.
• Aircraft 90 m above the pile top: 115 m above the pit floor beneath it.

That is legal, but the margin is 5 m - inside the combined error of a barometric altitude hold and downward-facing sensors over a smooth, low-texture surface. A sink of a few metres over the pile, or a rise over the pit floor, can put you over the limit without any warning you would notice.

The return-to-home setting is the bigger trap. If RTH height is set as an offset from the launch point and the launch point is on the pit floor, the aircraft will climb to that offset on link loss regardless of what is under it. Launch near the pit edge and the RTH climb can breach 120 m AGL over the floor, or descend into the pile if the offset is low.

Practical fix: cap the working height at around 70 m above pile tops so the worst case stays comfortably under 120 m, set RTH high enough to clear the piles and no higher, and confirm the offset reference before every sortie rather than trusting yesterday's setting.

The four-minute buffer is not real margin in these conditions. That 22-minute figure was almost certainly produced in still air; a 20 kt gust spread means the flight controller is working the motors continuously to hold position and hold height, and current draw climbs accordingly. A 15–25% endurance penalty in gusty, position-holding flight is not unusual, which is 3–5 minutes off a 22-minute figure.

Taken with the other pressures - a legal boundary through the survey area, a 5 m height margin over the piles, and a live helipad nearby - the sensible answer is no.

Restructure:

• Split into two sorties of about 9 minutes each with a battery change and a fresh look at the wind.
• Set the return trigger at 40% remaining, not 20%, so the reserve stays a reserve.
• Define a hard stop: if the average wind exceeds about 15 kt or the aircraft cannot hold position within a couple of metres, land and wait.

Explain to the client that the split costs ten extra minutes on the ground and removes the risk of an unplanned low-battery descent inside the ring.