Communication Failure and Contingencies

Oceanic airspace may offer fewer immediate vectors and less direct radio contact. The safe response creates lateral and vertical separation while the crew continues trying to obtain a revised clearance.

ADS and CPDLC service

CPDLC supports emergency alerting, pilot-to-controller downlink of position reports and clearance requests, controller-to-pilot uplink of clearances and instructions, and free text used only as a supplement to formatted messages. ADS automatically reports aircraft position, intent and selected meteorological information from the flight management system over VHF or satellite data link. Loss of service is announced as AUTOMATIC DEPENDENT SURVEILLANCE OUT OF SERVICE.

Emergency descent

The pilot navigates as necessary, advises the appropriate ATS unit and intentions when able, selects 7700 and the applicable ADS-B or ADS-C emergency indication, turns on exterior lights, watches for traffic visually and with ACAS, and coordinates further intentions when the descent is complete. ATC broadcasts ATTENTION ALL AIRCRAFT IN THE VICINITY OF (position) EMERGENCY DESCENT IN PROGRESS FROM (level), then gives specific instructions, clearances or traffic information. Keep the distress format brief here; Chapter 13 teaches it fully.

Unable to obtain prior clearance

Use MAYDAY or PAN PAN as appropriate and seek a revised clearance. If one cannot be obtained, initially turn at least 45 degrees left or right to establish a same-direction or opposite-direction track offset 15 NM from the assigned route. If unable to hold the assigned level, minimise the descent rate while offsetting and select a final altitude separated from normally used levels by 500 feet at or below FL 410, or 1,000 feet above FL 410. Broadcast identity, level, position, route or track and intentions on 121.5 MHz and, as backup, the inter-pilot air-to-air frequency 123.45 MHz. Keep exterior lights on, use ACAS and keep the transponder operating.

Strategic lateral offset and weather deviation

SLOP permits a right-of-centreline offset to reduce collision and wake exposure. Where route centreline spacing is 23 NM or more, the right offset may be selected in tenths up to 2 NM. Where spacing is 6 NM or more but less than 23 NM, the right offset may be selected in tenths up to 0.5 NM. For urgent weather handling, begin with WEATHER DEVIATION REQUIRED or PAN PAN. Advise ATC when the deviation is no longer required and when back on the cleared route.

Miscellaneous phraseology also covers hazards that interrupt an otherwise normal flight: wake turbulence, fuel dumping, low-level wind shear, low visibility, and the need to coordinate on an air-to-air channel.

Wake turbulence categories

Specified radar and non-radar wake minima must be maintained. Bali notes radar minima varying from 5 to 8 NM and non-radar time minima from 2 to 4 minutes. ATC separates IFR flights and, if necessary, gives instructions to regain wake separation. A pilot accepting a visual approach, or operating VFR, remains responsible for adequate distance from the preceding aircraft, though ATC passes relevant distance information. A departing aircraft receives take-off clearance only when the required wake minimum will exist after becoming airborne. ATC may say FOR WAKE TURBULENCE SEPARATION TURN LEFT HEADING, CAUTION WAKE TURBULENCE, THE RECOMMENDED DISTANCE IS (number) miles, EXTEND DOWNWIND DUE WAKE TURBULENCE, WAIT (number) minutes due wake turbulence, or HOLD POSITION DUE WAKE TURBULENCE.

Fuel dumping

The dumping aircraft broadcasts identity, type, level, starting point, track and length. Other traffic is warned to avoid the dumping area, including a vertical and lateral buffer. Completion is broadcast to all stations.

Low-level wind shear

ATC advises aircraft likely to be affected, informs the meteorological office and broadcasts the warning on ATIS for the next half hour unless later reports show that the hazard has ended. A pilot report gives callsign, the words WIND SHEAR REPORT, time, intensity, position and average height of the shear. The warning may say WIND-SHEAR WARNING, ARRIVING or DEPARTING, aircraft type, light, medium or heavy intensity, approach or departure runway, position, time and height of the wind-shear layer. The book treats low-level wind shear as extending up to 1,500 feet.

Inter-pilot communication, LVP and announcements

Aircraft beyond VHF ground coverage may use the designated inter-pilot channel, normally 123.45 MHz, by directed or general call. The initial call identifies the channel. Examples are SABENA NINE ZERO ONE, INDAIR FOUR ONE ONE, INTER-PILOT ONE TWO THREE DECIMAL FOUR FIVE, DO YOU READ? and ANY AIRCRAFT VICINITY OF a position followed by the calling aircraft and channel.

For low-visibility operations, ATC announces LPVS IN FORCE and later LPVS CANCELLED. Bali states that Category II or III operations require approval, a radio-altimeter decision height below 200 feet, suitable recording facilities and at least two crew members. LVTO applies when RVR is below 400 m, with specified operator minima. A passenger announcement states the operational cause and expected delay plainly without technical phraseology.

Before declaring failure, eliminate the simple causes. Then use whatever half of the radio link still works and make the aircraft's intentions predictable.

Air-to-ground checks

Confirm the correct route frequency, that the aeronautical station is open for watch, that the aircraft is within radio range and that receiver volume is correctly set. Check the selected box, headset, microphone, press-to-talk switch and installation. Try another suitable route frequency, another aircraft or another aeronautical station. If the transmitter may still work, send the message twice on the designated frequency, include the intended addressee and prefix it TRANSMITTING BLIND. If receiver failure is established, send reports twice at scheduled times or positions with TRANSMITTING BLIND DUE TO RECEIVER FAILURE.

ATC action and relay

The ground station checks its own primary, standby and emergency equipment, asks other stations and aircraft to try contact, and transmits blind on the frequency believed to be monitored. It gives the level, route and expected approach time or estimated arrival time it assumes the aircraft will follow, plus destination and alternate weather. To enlist another aircraft it may say REQUEST RELAY TO (station) or RELAY TO (station) followed by the message. A suspected transmitter failure can be tested with IF YOU READ (unit) followed by a manoeuvre or transponder instruction. ATC confirms TURN OBSERVED, SQUAWK OBSERVED or IDENT OBSERVED.

The safe flight path after complete failure depends first on whether visual conditions can certainly be maintained. If not, the procedure preserves the route, level and timing that ATC is most likely to protect.

VMC case

Select SQUAWK 7600. If in VMC and certain of maintaining VMC, remain in visual conditions, proceed to a suitable aerodrome, land, and report arrival by the most expeditious means to the appropriate ATS unit.

IMC or uncertain VMC case

Proceed according to the current flight plan confirmed by the last acknowledged ATC clearance. ATC assumes the aircraft climbs to the flight-planned level or the last level requested by the pilot and acknowledged by ATC.

Complete-failure checklist

Maintain terrain clearance, select 7600 or 7700 if an emergency also exists, try alternate published ATS frequencies, check communications equipment, listen to ATIS if possible, transmit reports and intentions blind twice, use landing, beacon and strobe lights, keep TCAS on and use available mobile or satellite telephone coverage to contact ATC.

Some contingencies demand communication that is both standardised and sensitive. A pilot may need to signal unlawful interference covertly, distinguish a fuel concern from distress, or respond to interception without ambiguity.

Unlawful interference

Select 7500 when unlawful interference prevents normal communication. The operational check is CONFIRM YOU ARE SQUAWKING 7500, spoken as CONFIRM YOU ARE SQUAWKING SEVEN FIVE ZERO ZERO. If the selection was accidental, the pilot responds NEGATIVE and corrects the code. In a genuine covert case, the pilot may be unable or unsafe to answer. ATC treats no reply as confirmation and may deliberately withhold repeated read-back or questioning so that the exchange does not alert the person interfering. If safe and able, use HIJACK or an appropriate distress message, but personal safety governs.

Minimum fuel and fuel emergency

Strayed and unidentified aircraft

A strayed aircraft has deviated significantly from its intended track or reports that it is lost. An unidentified aircraft is observed or reported in an area but its identity has not been established. The pilot of a strayed aircraft calls ATS, reports identity, position if known, level, conditions, last known point and intentions, and requests navigation assistance. ATS attempts identification and position fixing, warns other units, provides headings or navigation help and coordinates with military authorities when required.

Interception of civil aircraft

Monitor 121.5 MHz. The intercepting unit calls INTERCEPT CONTROL; the civil aircraft is the INTERCEPTED AIRCRAFT. Follow international visual signals and avoid abrupt manoeuvres unless required for safety.

The final group of miscellaneous procedures deals with congested frequencies, large communication disruptions and abnormal situations that still require a concise operational request.

Simultaneous or continuous transmissions

A blocked transmission can occur when two stations speak together or a transmitter remains keyed. A pilot who hears the overlap can help by naming the blocking station: DELHI TOWER, SPICE JET TWO SIX FIVE, TRANSMISSION BLOCKED BY VAL, SAY AGAIN. If only part is required, add SAY AGAIN ALL AFTER the last correctly received word or phrase.

Traffic information broadcasts by aircraft

TIBA provides pilot-to-pilot information after a significant disruption of air traffic or telecommunication service. Use it for position, level, track, intentions, weather deviations and traffic conflict information on the published frequency. Listen before transmitting and use an all-stations address when the intended aircraft is unknown.

Worked R/T situations

Other equipment and communication degradations

Report the failed navigation function exactly, such as UNABLE RNAV DUE EQUIPMENT. If GNSS is unreliable or unavailable because of interference, RAIM loss, SBAS or GBAS outage, use the corresponding status phrase and revert to an available approved means of navigation. For ADS, CPDLC, Mode C or RVSM failure, state the affected system and accept revised separation or routing. For a blocked call, do not guess the missing clearance.

Passenger announcement

The captain may make a plain-language PA announcement giving the delay, operational reason and an apology. It is separate from ATC phraseology and should not reveal sensitive operational information.