SINGAPURCANAC,
It is not big problem if r/t works properly but what happen and how you deal in cases of two way radio communication failure.
Two-way radio failure is exactly why this rule exists. If your radio doesn't fail, DON'T USE THIS PROCEDURE! You can find the full story in 14 CFR 91.185 (AKA FAR 91.185).
Sec. 91.185 - IFR operations: Two-way radio communications failure.
(a) General. Unless otherwise authorized by ATC, each pilot who has two-way radio communications failure when operating under IFR shall comply with the rules of this section.
(b)
VFR conditions. If the failure occurs in VFR conditions, or if VFR conditions are encountered after the failure, each pilot shall continue the flight under VFR and land as soon as practicable.
(c)
IFR conditions. If the failure occurs in IFR conditions, or if paragraph (b) of this section cannot be complied with, each pilot shall continue the flight according to the following:
(1) Route. (i) By the route assigned in the last ATC clearance received;
(ii) If being radar vectored, by the direct route from the point of radio failure to the fix, route, or airway specified in the vector clearance;
(iii) In the absence of an assigned route, by the route that ATC has advised may be expected in a further clearance; or
(iv) In the absence of an assigned route or a route that ATC has advised may be expected in a further clearance, by the route filed in the flight plan.
(2) Altitude. At the highest of the following altitudes or flight levels for the route segment being flown:(i) The altitude or flight level assigned in the last ATC clearance received;
(ii) The minimum altitude (converted, if appropriate, to minimum flight level as prescribed in
§91.121(c)) for IFR operations; or
(iii) The altitude or flight level ATC has advised may be expected in a further clearance. [All bold lines are my emphasis]
Thus, if your coms go away, you wait 10 minutes after departure and climb to your "expect" altitude. That's what the controller is "expecting" you to do! If your coms are not lost, you simply follow the controller's instructions. If I'm not mistaken, the ICAO methodolgy is similar:
From ICAO Annex 2:
...
3.6.5.2 Communication failure...
3.6.5.2.2 If in instrument meteorological conditions or
when the pilot of an IFR flight considers it inadvisable to complete
the flight in accordance with 3.6.5.2.1 a), the aircraft
shall:
a) unless otherwise prescribed on the basis of regional air navigation agreement, in airspace where radar is not used in the provision of air traffic control, maintain the last assigned speed and level, or minimum flight altitude if higher, for a period of 20 minutes following the aircraft’s failure to report its position over a compulsory reporting point and thereafter adjust level and speed in accordance with the filed flight plan;
b) in airspace where radar is used in the provision of air traffic control, maintain the last assigned speed and level, or minimum flight altitude if higher, for a period of 7 minutes following:
1) the time the last assigned level or minimum flight altitude is reached; or
2) the time the transponder is set to Code 7600; or
3) the aircraft’s failure to report its position over a compulsory reporting point; whichever is later, and thereafter adjust level and speed in accordance with the filed flight plan;
[snip]
Hope that clears that up a little bit.
Dave