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Weather deviations, contingencies and communications failure

This page is a plain-language summary of NAT Doc 007 (V.2026-1), Chapters 5.6 and 10. On VATSIM, always tell the controller what you are doing as soon as you can. If the controller gives you an instruction, follow it. The steps below only apply while you are waiting for one.

Weather deviations

You must have an ATC clearance to leave your track or route, even for weather.

  1. Ask early. Contact the controller by CPDLC or voice as soon as you can, and say how far off track you want to go (for example "request deviation up to 20 miles left of track because of weather"). If it is urgent, say "WEATHER DEVIATION REQUIRED" to get priority on the frequency. Use "PAN PAN" (preferably three times) if the situation calls for it.
  2. The controller will either:
    • clear you to deviate, or
    • tell you they cannot, tell you about conflicting traffic and ask what you intend to do.
  3. Tell ATC when you are back on track. Also tell them if the deviation is no longer needed.

If you cannot get a clearance in time

You are the pilot in command, and safety comes first. Keep trying to reach ATC, and meanwhile:

  • If possible, turn away from the organised track system.
  • Broadcast your callsign, flight level, position (including the track letter) and intentions on the frequency in use and on 121.500. Use 123.450 as a backup.
  • Watch for other traffic, and use ACAS if you have it. Turn on all exterior lights.
  • For a deviation of less than 5 NM, stay at your assigned level.
  • For a deviation of 5 NM or more, change level by 300 ft when you are about 5 NM from track, as in the table below.
  • Be back at your assigned level when you are within about 5 NM of track on your way back.
Cleared track direction Deviating Level change
Eastbound (000°-179° magnetic) Left Descend 300 ft
Eastbound (000°-179° magnetic) Right Climb 300 ft
Westbound (180°-359° magnetic) Left Climb 300 ft
Westbound (180°-359° magnetic) Right Descend 300 ft

In-flight contingencies (cannot continue as cleared)

If you cannot keep to your clearance (for example, an engine problem or pressurisation failure), get a revised clearance if you can before you do anything else. If you cannot:

  1. Turn at least 30 degrees left or right, and then fly a track parallel to your route, 5 NM offset. Choose the direction with the nearby tracks and traffic flow in mind, or toward your alternate.
  2. Fly at a level and offset where other traffic is less likely to be. If you can, hold your level until you are established on the offset. If not, keep your rate of descent as low as you can.
  3. Once on the offset, either descend below FL290 and apply a 500 ft offset from the normal levels, or stay where you are and apply a 500 ft offset (1,000 ft above FL410).
  4. Turn on all exterior lights, keep ACAS on, and squawk 7700 if you can.
  5. Tell ATC as soon as you can, and say "MAYDAY" or "PAN PAN" (preferably three times) if you use the radio.
  6. Broadcast your callsign, the nature of the problem, your intentions, position (with the track letter) and flight level on 121.500 (with 123.450 as a backup) and on the frequency in use.

Communications failure

Poor HF conditions

HF can be disturbed by solar activity, which is most common near the poles. Try a different HF frequency. If you cannot reach your radio station, try another station and ask them to relay for you. ATC may not be able to provide the same service during an HF blackout, so be careful even if you are using CPDLC.

If you cannot reach ATC

  • Use CPDLC if you have it.
  • If you have SATVOICE, use the telephone number or short code published for the facility.
  • Try VHF to call any other ATC facility or another aircraft, tell them of the problem, and ask them to relay.
  • Use 123.450 to relay your position reports through other aircraft. You may use 121.500 to make first contact, then move to 123.450.
  • Broadcast your position regularly on 123.450 until you re-establish contact.
  • If you lose all two-way communication (VHF, HF, CPDLC and SATVOICE), squawk 7600.

On VATSIM

If you lose voice or text for technical reasons, say so in text chat to the controller, and give your intentions. Real-world rules (such as continuing on your last clearance) vary by state, so follow the controller's instructions where you can.

Sources

NAT Doc 007 (V.2026-1), 5.6 Communications Failure, 10.2-10.4 Contingency and Weather Deviation Procedures.

Last update: November 14, 2026