From the UK IAP ENR 1.1
5.3 Activities of a Dangerous Nature
5.3.2 High Intensity Radio Transmission Area (HIRTA) - Airspace of defined dimensions within which there is radio energy of an intensity which may cause interference with and on rare occasions damage to communications and navigation equipment.
Areas within which there is radio energy of an intensity which could cause interference with and on rare occasions, cause damage to, communications and navigation equipment such as Radio Altimeter, VOR, ILS and Doppler are listed at ENR 5.3. The intensity may be sufficient to detonate electrically initiated explosive devices carried or fitted in aircraft.
Only the most significant sources are listed and in some of these areas the intensity of the radio energy may be such that it would be injurious to remain for more than one minute in the immediate vicinity of the energy source. This is especially relevant to helicopter operations and the list contains appropriate warnings; however it would be prudent for helicopter pilots to avoid lingering closer than 100 m to any radar aerial. Pilots approaching oil production platforms on which dish aerials can be observed should, wherever possible, approach from a direction out of the general line-of-shoot of such aerials.
Airborne Early Warning (AEW) aircraft operate within United Kingdom airspace and due to possible radiation hazards, all aircraft should maintain a minimum separation of 1000 m lateral and 1000 ft vertical from such aircraft. AEW aircraft can be identified as follows:
(a) RAF/NATO/USAF E-3 - a Boeing 707 with a large rotodome mounted on the upper fuselage (E-3 Orbit Areas are listed at ENR 5.3);
(b) USN E-2C - a medium size twin turboprop with a four-finned cantilever tail and a large rotodome mounted on the upper fuselage.