CONSOLIDATED B-24 LIBERATOR RADIO ALTITUDE LIMIT SWITCH

The General Electric ID-14/APN-1 Radio Altimeter Altitude Limit Selector Switch, was a component of the US designed AN/APN-1 radio set, used to measure and indicate to the pilot his altitude over the terrain during flight.

This was particularly critical for USN aircraft such as the TBF Avenger torpedo bomber and the SB2C Helldiver as well as the USN’s marinised B-24 Liberator submarine hunter in maintaining an accurate and consistent launch height for their attacks on enemy surface shipping and submarines.

As part of the British/US Lend Lease Agreement, both the British Coastal Command and Australia’s RAAF also used the AN/APN-1 in their marine attack aircraft such as the Fairey Swordfish, Bristol Beaufort, Bristol Beaufighter, Catalina Flying Boats and later in the war, the marinised B-24 Liberartor.

The AN/APN-1 radar altimeter which was designed to emit a downward signal from the aircraft's transmitter antenna.

As the terrain changed in hight and composition with the rise and fall of the aircraft's flight, a 'bounced' return signal would be received by a separate receiver antenna. The difference in signal frequency and time interval from send and receive gave a highly accurate height reading.

The timing and correct height of torpedo or dive bomb release was crucial to ensure the weapons had enough time to self arm and hit their targets.

An Altitude Selector Switch, which sat beside the Altitude Limit Selector enabled the pilot or bomb aimer to set the lower altitude limit. If the aircraft descended below this limit a red light would illuminate on the panel while a green light indicated the aircraft was too high. A yellow light indicated the correct selected height.

The US Navy had  acquired many B-24Ds from the USAAF for their anti-submarine operations, and also 977 of the PB4Y-1, which were either converted from the B-24D with the addition of an Erco nose turret, or from the B-24J, B-24L, or B-24M with a Consolidated nose turret. 

Later came 736 of the much-modified PB4Y-2, with supercharged engines, single tail, two upper turrets, no ball turret, twin guns in each waist position, an extra 2.1 m added to the length of the fuselage, and many other improvements. The PB4Y-2 was so modified that it got a different name, being called Privateer.

The centre knob of this instrument still turns to set the altitude between 50 to 300ft and while there is some minor paint chipping on the outside dial, the glass, display and case are in excellent condition. 

This B-24 Consolidated Liberator Instrument comes complete with detailed Scale Model, Mango Wood Stand & Plaque plus Printed Fact Sheet featuring photo of instrument in aircraft cockpit. 

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