Lost communications & transponder codes

Transponder codes

Lost communications (IFR, in controlled airspace)

Attempt contact on other frequencies, via other aircraft, or by other means; select 7600 on the transponder.
If in VMC: continue in VMC, land at the nearest suitable aerodrome, and report arrival by the most expeditious means.
If in IMC: continue per the flight plan — the route and level last assigned, or if none, as filed — then commence descent/approach at the Expected Approach Time (EAT) if one was given, otherwise at the ETA from the flight plan.
You must land within 30 minutes of that ETA, or the last EAT received, whichever is later.
Squawk 7600 as soon as a communications failure is recognized, so ATC can apply their own lost-comm procedures.

Expected Approach Time (EAT)

The time ATC estimates an aircraft delayed by 10 minutes or more can leave the holding fix to begin its approach — not a clearance, but what ATC expects to be able to grant.
Issued when a delay of 10 minutes or more is expected, or an anticipated hold of 30 minutes or more.
A revision of 5 minutes or more from a previously given EAT should be passed to the aircraft as soon as possible.

Source: SERA.8020 / ICAO Annex 2 Appendix 2, Doc 4444 §6.5.7 – Communication failure & EAT