FM or PCM Whats the diff
We need to define 'Failsafe' and 'Hold' to understand what actually happens during a period of interferance or loss of signal.
'Fail safe' is a condition that exists on one or more of the channels when no recognized signal is being rx'd by the PCM part of the rx.. - It is programmable, and drives the selected channel(s) to a user define position - i.e. throttle low
'Hold' (sometimes wrongly referred to as 'lock out') is a condition that also exists on one or more channels, again when no recognized signal is being rx'd by the PCM part of the rx, the channel(s) hold their last good position.
What is important to note, is that as soon as a recognized signal is rx'd (i.e interference stops or reduces), these conditions no longer exists, and control normal is resumed. These conditions, do not 'trip in and stay in' - providing the interference ceases; or it's volume reduces so the PCM signal is dominant.
Also, it is also important to note, that most modern PCM systems, will allow a mix of 'fail safe' channels, and 'hold' channels.
If anyone is in doubt as to how their particular radio system will behave during a 'hit', set up a system on the work bench, and experiment with 'failsafe' and 'hold' and note the results; to simulate a 'hit' or loss of signal, turn off the tx or switch on another on the same freq. Obviously do this on the work bench at home - not whilst flying!!!
Also its worth noting and asking what are we are trying to achieve with our Radio gear? Well, safe reliable guidance of our model is the obvious answer, we could also, mention stuff such as confidence, cost, versatility, etc etc, but what we are not going to do (well not yet anyway) is to get a system that will protect us from someone else switching on on our chosen freq. If someone does it's probably curtains anyway whether it be PPM / PCM dual con / single con etc. No rc system will be immune from that , nor indeed are today's current systems designed to do that (although I believe Multiplex are about to 'break the mould' with their new 12, yes 12 channel 'intelligent tx' system) - to stop 'shoot downs' we put our faith in a humble 20 pence peg, and some good discipline!!
Hope this adds to the debate!!
See ya
;-)