LOCKHEED PV1 VENTURA, GENERAL ELECTRIC ID-14/APN-1 RADIO ALTITUDE LIMIT SELECTOR SWITCH

The General Electric, Radio Altitude Limit Switch was a component of US Navy’s Radar Bombing Navigational Computer AN/APA-61was the US Navy's primary airborne frequency modulated, 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.

Being able to both preset and maintain the aircraft's correct height for its torpedo or dive bomb release was critical to ensuring the weapons had enough time to self arm and hit their targets. 

To accomplish this, the pilot used two, cockpit-mounted instruments which worked in tandem with the aircraft’s radio transmitter and receiver

The first was the General Electric, Radio Altitude Indicator (ID-236/APA-61), which the pilot preset to the designated release height required for either a bombing or torpedo run to the target. (Seen here on the left).

The second instrument was the General Electric, Radio Altitude Limit Selector Switch (SA-1/ARN-1), by which the pilot was able to set the lower altitude limit for the target approach. (Shown here on the right).

If the aircraft descended below this limit, a red light would illuminate on the pilot’s flying panel. If the aircraft was too high, a green light would show. 

It was only when the aircraft was flying at the correct altitude, that the pilot would see a yellow light appear - indicating he was on target for the release.

The combined system provided a dual range indicator of 0-400 feet and 400-4000 feet; and had an accuracy within plus or minus 6 feet on the 400-foot range and within plus or minus 60 feet on the 4000-foot range.

The lower part of the Radio Altitude Limiter Selector Switch can just be seen here on the right in this cockpit photo, in front of the PV1 pilot's control column with its paired Radio Altitude Indicator more clearly visible - mounted just above and in front of the control column.

The Radar Bombing Navigational Computer AN/APA-6 was fitted to most of the USN’s carrier-launched and marine patrol aircraft.

These included the SBC2 Helldiver, Grumman TBF Avenger, Douglas SBD Dauntless as well as the PBY Catalina and PV1 Ventura.

It was also used by the USAAF in many of their low level strike aircraft such as the B-25 Mitchell, Douglas A-20 Havoc A26 Invader and Lockheed Hudson.

As part of the US/British Lend Lease programme, the system was also used in the British De Havilland Mosquito and the Bristol Beaufighter and carrier-launched Fairey Swordfish torpedo bombers.

What a special gift for the aviation enthusiast in your life!  - An original, WWII PV1 Ventura, General Electric Radio Altitude Limit Switch mounted in its 100yr old Mango Wood Display Stand with engraved Plaque, printed and laminated Fact Sheet plus a highly detailed, custom-built 1/72 or more detailed 1/48 scale Model of this iconic US built bomber perched atop its magnetic display arm.

This Lockheed PV-1 Ventura 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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