III. Area Control Service
office, or the aerodrome control tower concerned shall forward further clearances to all aircraft involved as to additional procedures to be followed during and subsequent to the emergency descent.
17. Air-ground communication failure

17.1 Action by air traffic control units when unable to maintain two-way communication with an aircraft operating in a control area or control zone shall be as outlined in the paragraphs which follow.
17.2 As soon as it is known that two-way communication has failed, action shall be taken to ascertain whether the aircraft is able to receive transmissions from the air traffic control unit by requesting it to execute a specified manoeuvre which can be observed by radar or to transmit, if possible, a specified signal in order to indicate acknowledgement.
17.3 If the aircraft fails to indicate that it is able to receive and acknowledge transmissions, separation shall be maintained between the aircraft having the communication failure and other aircraft, based on the assumption that the aircraft will:
a)  if in visual meteorological conditions:
i) continue to fly in visual meteorological conditions;
ii) land at the nearest suitable aerodrome; and
iii) report its arrival by the most expeditious means to the appropriate air traffic control unit; or
b)  if in instrument meteorological conditions or when conditions are such that it does not appear feasible to complete the flight in accordance with 17.3 a):
i)  unless otherwise prescribed on the basis of regional air navigation agreement, 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;
ii)  proceed according to the current flight plan route to the appropriate designated navigation aid serving the destination aerodrome and, when required to ensure compliance with iii) below, hold over this aid until commencement of descent;
iii)  commence descent from the navigation aid specified in ii) at, or as close as possible to, the expected approach time last received and acknowledged; or, if no expected approach time has been received and acknowledged, at, or as close as possible to, the estimated time of arrival resulting from the current flight plan;
iv)  complete a normal instrument approach procedure as specified for the designated navigation aid; and
v)  land, if possible, within thirty minutes after the estimated time of arrival specified in b) or the last acknowledged expected approach time, whichever is later.
Note 1.— Provisions related to minimum levels are contained in Annex 2, 5.1.2.
Note 2.— As evidenced by the meteorological conditions
prescribed therein, 17.3 a) relates to all controlled flights,
whereas 17.3 b) relates only to IFR flights.
17.4 Action taken to ensure suitable separation shall cease to be based on the assumption stated in 17.3 when:
a)  it is determined that the aircraft is following a procedure differing from that in 17.3; or
b)  through the use of electronic or other aids, air traffic control units determine that action differing from that required by 17.3 may be taken without impairing safety; or
c)  positive information is received that the aircraft has landed.
17.5 As soon as it is known that two-way communi-cation has failed, appropriate information describing the action taken by the air traffic control unit, or instructions justified by any emergency situation, shall be transmitted blind for the attention of the aircraft concerned, on the frequencies available on which the aircraft is believed to be listening, including the voice frequencies of available radio navigation or approach aids. Information shall also be given concerning:
　
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