I have failsafe on throttle and elevator , power to idle and up elevator.
Today while I was doing a low pass it went into failsafe no more than 200 feet away, the sudden climb and closed throttle un mistakable.
It reconnected straight away and I landed dead stick.
When I had a look at the 10 channel receiver the led was orange.
What exactly does this indicate? Did the voltage drop and cause the failsafe or is this a loss of signal that caused it and would the led go orange if there was a loss of signal?

If it's just solid orange (and you have newer firmware) then it was a low power condition. If it has older firmware then it could be that you completely lost power and when it came back it dropped again and triggered the low voltage warning. The newer firmware will flash orange if the system rebooted. You can test if you have the newer firmware by power up everything so servos move and then remove power from the receiver and then turn it back on. If your LED flashes orange, then you have the latest firmware with the reboot warning. If the LED comes back on as green, then you have the older firmware.

In any case, you need to figure out what caused your voltage to suddenly drop like that!

Have you done a range test lately?

I did some testing last night. I had made up a voltage reducer(6.2v) for my Life 2s pack, of 2 6a diodes in parallel with a third the other way round for current flow back to battery.
I think there is something in this set up that allows the voltage to drop from the back flow from the servo motors. After moving all servos several times I could sometimes get the tattletale to detect 4.5 v from a 1700 6.6v Life pack. I have removed it now and will fly with the 6.6v and have fitted a nano. I will do the test you described and see what version I have.
You would know more about this than me but I suspect the back emf from the servo motors have caused a voltage drop.

What LiFe pack are you using? 1700mAh is not an A123 brand size, so it could be the C rating is very low (like a Nimh) and you really are seeing a voltage drop under some load. I am not a fan of diodes used for dropping voltage. The recovery period would have to be very fast (nanoseconds), and you really would need some caps before and after the diodes in order for that type of circuit to work properly.

I have just returned from flying field and flew "without the diode" on 6.6v using an 8 Channel receiver.
I range tested it at 50 paces ok.
It went to failsafe twice, in one flight, motor to idle and climbed no mistake and regained the link again. It was side on at 200 meters away, the 8 channel led was still green when I landed.
I turned the rx power of and on again with the TX still on and the led went flashing orange. So that would indicate it was not a power problem.
The Lifes are 1700 20c Turnigy so should be good for 35A at least short burst and I checked with tattletale first. I changed the receiver at the field to a nano and had 2 more flights without any signs of a brown out. I am thinking maybe the 8 &10 channels are not sensitive enough or I have a problem in the TX (JR10x). Ithink I will try my MX22 and see if the brown outs happen again on some old planes.

50 paces is not enough. Please follow the range test procedure found in the sticky thread here.

50 paces is about 150 feet when I pace it out, and I thought that would be enough.
How much more sensitive would the nano and RFU be over the 8 &10 channel ? If you can"t get the range in the test, what can you do to improve it. Are there any guide lines to get better reception other than keep metal and wires away from the antenna . Ariel pointing up or down etc.

Yes, but you are not following the range test procedure if you really only went 150 feet. You must continue walking until no control is found and then release the PROG to see if control is immediate (and perfect). Intermittent control would be a problem.

The range of the original 8/10 channel receivers is about 5 miles max. The Nano and RFU are 25% better, with the RFU having not much change at any orientation.

You might also want to check the center pin on the transmitter module and also look at your antenna. The antenna should be tight when it folds and does not spin easily once the base is firmly screwed in.

Do you have pics of your installation? Moving wires around the antenna can definitely cause a momentary lockout like you describe.

I checked the pin and its level and antenna is good I never twist it or remove it.
I checked the solder joints on the pins for the module and they are fine no cracks.
I checked tx on txdiag and the version is 4.2 and signal strength 37.
I have ordered some RFU+ 10+ and some nanos and will retire the 8 &10 s.
I am very careful to keep wires away from antenna with cable ties and Velcro and do not use switches. So frustrating loosing 3 planes, 2 coming into land head on and I side on, flying down wind, no ARF, all scratch built warbirds.

Do you have any pics of installations? What are you using for power? switches?

I have taken out the 8 channel and replaced it with a nano but you can see where it goes, 2 feet away from the gas motor, located in a foam pocket away from anything metal. Battery was a 1700 Life 6.6v no switch, JST plug straight into receiver via 2 JR plugs one in bat and the other in ch 8. The model is a 1/3 scale volksplane . All the leads were bundled together and ran out way from Ariel . The receiver is as you can see well away from every thing in the head rest and you could not get a better position for it.