A warning today, the full approach check in development

Frequently Asked Questions

Which surface is checked?

Today, the Annex 14 approach surface, as a warning in flight planning for the obstacles in the register. That is not the PAPI obstacle protection surface. The protection surface is what Annex 14 defines for the visual approach slope indicator on that runway end. It starts a short distance in front of the threshold at a set width, diverges outward on both sides at a fixed rate and climbs along the approach at an angle slightly below the glide path the PAPI is set to. A check against it is in development. Because the plane is built from the runway geometry and the set angle, it can be constructed exactly, and anything above it is by definition a penetration.

How is this different from an obstacle limitation surface survey?

In extent. A protection surface check covers the plane over one approach, which decides whether a crew following the PAPI has anything in its way. An obstacle limitation surface evaluation covers the whole set of surfaces around the aerodrome, approach, take-off climb, transitional, inner horizontal and conical, reaching kilometres out, and is what an operator owes the authority as a statement of the aerodrome's surroundings. TarmacView does not offer that full evaluation yet, and it is in development. Only the approach surface is tested today.

Why fly it if we have a surveyed obstacle register?

Because the register tells you what was surveyed on the day it was surveyed. A complete check tests every object in it against the surface as a computation, before anyone flies, and names any that penetrate. What the register cannot contain is the objects nobody surveyed, the tree that grew, the mast that was not notified, the temporary crane. A flight along the surface is what finds those. Today TarmacView does the first half for the approach surface, as a planning warning. The flown half is in development. The register alone is a statement about the past.

How does a flown arc prove the surface is clear?

The drone flies an arc out on the approach at the height the surface plane reaches at that distance, with the camera locked on a point on the extended centreline that also lies on the plane. The sightline from the camera to that point therefore lies in the surface, and anything rising through the surface between the two passes in front of the camera. The sweep either side of the runway axis covers the sector a crew uses. This is the method, and flying it for obstacles is in development and not available today.

What do we get for a penetration?

Today, a warning in flight planning that the obstacle penetrates the Annex 14 approach surface, and the obstacle's record in the register, with its polygon, type and heights. The register can be exported on the airport data sheet as JSON, CSV or PDF. It is a warning, not a report, and the heights are the registered values rather than measurements from imagery. What you do not get is the decision about whether the PAPI can stay in service in the meantime. That is the operator's and the authority's, and it usually depends on how far the penetration is from the on-slope signal.

How often should the approach be checked?

Often enough that a penetration is caught before an inspector or a pilot report catches it. A poplar can add a metre a year, and a line of them at the edge of the approach can cross a surface that slopes at a few degrees within a couple of seasons. Aerodromes with woodland under the approach tend to check annually, in winter when the canopy is at its lowest. Aerodromes with cleared surroundings check when something changes: a permit, a crane, a works handover, a re-aimed PAPI. Keep the obstacle register current between checks, because the warning in flight planning is only as good as the register.