// Light signals
Signal lamp and the Aldis
The tower signal lamp, from the wartime Aldis to today’s light gun: the red, green and white signals, what they mean, and how pilots acknowledge.
What it is
- CAP 670 requires a signal lamp with white, red and green lenses plus a spare bulb, usable over the whole manoeuvring area and circuit (IAS01.40). CAP 493 applies SERA.3301.
How controllers use it
- Pilots acknowledge in flight by rocking the wings (day) or flashing landing lights twice (night); on the ground by moving ailerons or rudder (day) or flashing lights (night).
UK rules and practice
- A UK civil table of light signals to vehicles was not found. The military RA 3262 uses: green flashing = cleared to proceed; steady red = stop; red flashing = clear the runway/taxiway immediately; white flashing = return to starting point or as briefed. The US FAA table differs, so don’t mix the two.
At Prestwick
- AIP: “Except for light signals, ground signals are not displayed.”
| Signal | In flight | On the ground |
|---|---|---|
| Steady green | Cleared to land | Cleared for take-off |
| Steady red | Give way, continue circling | Stop |
| Green flashes | Return for landing* | Cleared to taxi |
| Red flashes | Aerodrome unsafe, do not land | Taxi clear of landing area in use |
| White flashes | Land at this aerodrome and proceed to apron* | Return to starting point |
| Red pyrotechnic | Notwithstanding previous instructions, do not land for the time being | — |
// Through the eras
| Era | Status | Notes |
|---|---|---|
| 1930s–40s | Typical UK practice | An Aldis-type lamp was standard flying-control kit (a public-domain RAF photo shows one in use at Imphal; none of Prestwick itself was found). |
| 1950s–60s | Typical UK practice | A signal lamp on a hook or bracket in the cab is typical. |
| 1980s–90s | Typical UK practice | Required cab equipment (CAP 670). |
| Modern | At Prestwick (sourced) | The AIP says that “except for light signals, ground signals are not displayed”, so the lamp remains the visual backup. |
// Photographs
