14 CFR § 91.185

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.

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.

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:

Route. (i) By the route assigned in the last ATC clearance received;

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;

In the absence of an assigned route, by the route that ATC has advised may be expected in a further clearance; or

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.

Altitude. At the highest of the following altitudes or flight levels for the route segment being flown:

The altitude or flight level assigned in the last ATC clearance received;

The minimum altitude (converted, if appropriate, to minimum flight level as prescribed in § 91.121(c)) for IFR operations; or

The altitude or flight level ATC has advised may be expected in a further clearance.

Leave clearance limit. (i) When the clearance limit is a fix from which an approach begins, commence descent or descent and approach as close as possible to the expect-further-clearance time if one has been received, or if one has not been received, as close as possible to the estimated time of arrival as calculated from the filed or amended (with ATC) estimated time en route.

If the clearance limit is not a fix from which an approach begins, leave the clearance limit at the expect-further-clearance time if one has been received, or if none has been received, upon arrival over the clearance limit, and proceed to a fix from which an approach begins and commence descent or descent and approach as close as possible to the estimated time of arrival as calculated from the filed or amended (with ATC) estimated time en route.