(b)  
a flight plan (FP) has been filed and no arrival report has been received by the area control centre (ACC)

(i)  
within 1 hr after the estimated time of arrival (ETA) last notified to or estimated by the ACC, whichever is later;

(ii)
at the search and rescue (SAR) time requested by the originator,whichever is earlier;

(c)
a flight itinerary (FI) has been filed and no arrival report has been received by the ACC

(i)  
within 24 hrs after the latest ETA; or

(ii)
at the SAR time requested by the originator, whichever is earlier;

(d)  
an FP or FI has been filed and it is determined that no arrival report can be expected either because there is no communication system serving the point of arrival or the system serving the airport is inoperative.

.  see also: emergency phase
Fr: phase d’incertitude
(2) ICAO: A situation wherein uncertainty exists as to the safety of an aircraft and its occupants.
.
abbreviation: INCERFA

.
see also: emergency phase

Fr: phase d’incertitude
uncontrolled aerodrome An aerodrome at which a control tower has not been established. This designation also applies during the non-operational period when an established control tower is on reduced hours (part time). Fr: aérodrome non contr.lé
uncontrolled airspace
Class G and specified Class F airspace within which ATC service is not provided.
Fr: espace aérien non contr.lé
under the hood An expression indicating that the pilot is using a hood to restrict visibility outside the cockpit while simulating instrument flight. An instrument-rated pilot is required in the other control seat while this operation is being conducted. Fr: sous la visière
under way The state of being on the surface of the water but not moored or fastened to any fixed object on the land or in the water.  Fr: en marche
UNICOM Abbreviation for: universal communications Fr: UNICOM
uninhabited aerial vehicle Other expression for: unmanned aerial vehicle
. abbreviation: UAV
uninhabited air vehicle Other expression for: unmanned aerial vehicle
. abbreviation: UAV
uninterruptible power supply In ATS operations, a power system that is not subjected to any interruption when a break occurs in the normal power supply. Note: A UPS is required for precision approach CAT II and precision approach CAT III instrument landing system (ILS) operations.
. abbreviation: UPS
Fr: alimentation sans coupure
universal Spoken expression for: Co-Ordinated Universal Time . other spoken expression: zulu Fr: universel
universal communications An air-ground communication facility operated by a private agency to provide private advisory station (PAS) service at uncontrolled aerodromes and airports with no ATS air-ground communication facility.