Old transponder TSOs
Anyone got a copy of the now obsolete TSO-C74, TSO-C74a or TSO-C74b?
In particular, does TSO-C74b require the transponder to reply to Mode C interrogation with framing pulses, even though no information pulses are sent, and what were the corresponding requirements in TSO-C74 and TSO-C74a?
For reference, the relevant bits in TSO-C74c are
2.4 Interrogation. The equipment must accept and reply to interrogations on at least Modes 3/A and C
2.14 Pressure-Altitude Transmission. ... The transponder must be provided with a means to remove the information pulses from the Mode C reply when requested by Air Traffic Control. The transponder must continue transmitting the framing pulses on Mode C when the information pulses have been removed or are not provided.
Thanks