[ARC5] IFF Destructor Firing Circuit Potential Warning Light Panel BC-767

[Mike Morrow]

Paul asked:

> Can anyone identify the function of a BC-767?  It's called out in the 
> radio installation of our 1943 Curtiss P-40M aircraft as an "indicator".
> To the best of my knowledge it had something to do with the destructor
> used to destroy the IFF radio gear installed in the rear fuselage in
> the event of a crash landing behind enemy lines...

The BC-767 is a small panel with two redundant lights that was mounted
near the IFF RT unit for the SCR-515-A, SCR-595-A, or SCR-695-A.  If
the lights were on, then that showed that IFF unit destructor firing
potential existed at the airplane connector into which the destructor
would be plugged.  The main purpose was to warn the radio technician
NOT to connect the destructor into the circuit, since doing so would
cause destructor activation.  That would be uncool, because that would
destroy the IFF set and/or hazard personnel.

The firing circuit could have potential if the impact switch had tripped,
or the two series-connected manual firing pushbuttons on the BC-765 panel
at the pilot's position were depressed, or some circuit short/malfunction.

These show up on ebay quite frequently.

> and may have been purposely misidentified in the blueprints to prevent
> enemy espionage of the IFF technology. I know this occurred as the
> "destructor" (explosive device installed in the fuselage is identified
> as "fire extinguisher crash switch" and the pilot's manual does not
> refer to the IFF set other than to call it "a supplemental communication
> radio".

The SCR-595-A IFF was simply a US Navy ABK Mark III IFF, without any
Army nomenclature applied to the RT unit.  The SCR-695-A Mark III/G IFF
unit was the BC-966-A.  The nameplates of all of these units bore the
description of "RADIO RECEIVER" to mislead the other side.  But the USN
ABK units also bear USN component numbers starting with "43" which is
the component code for a "receiver-transmitter."  Not too consistent
or deceptive!

Dave commented:

>Is this the impactor switch thing...I always wondered how they kept from
>blowing the destruct during tight turns.

That was the BC-706.  The USN had an equivalent.  IFF destruct systems
were used in all the USAAF and USN IFFs at least to the USN AN/APX-2
series.  The common post-war AN/APX-6 IFFs, which were still to be
found on B-52 and many other USAF aircraft as part of the AN/APX-25
into the 1970s, had destructor unit capability.  I don't know if it
was still being used that late, though.  The Vietnam-era AN/APX-44 and
AN/APX-72 IFFs didn't have destructors.

There are a lot of stories about hard landings causing the activation of
the impact switches.  I think it was customary in B-24 and other aircraft
to disconnect the destructor cable just prior to landing, when practicable.

Mike / KK5F