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Can you confirm whether this statement is true for civil and/or military aviation?

When the radio is inoperative in flight and there is an emergency, pilots can attract attention from ATC by flying a triangular pattern.

I was able to find related information online. A triangular distress pattern:

  • Is (or was) apparently used by US Navy (page I-7).
  • Is mentioned in this UK GA forum:

    Coms failure procedure for a Radar ATSU to arrange a shepherd aircraft to guide you to a suitable airfield is to set 7600 and try 121.50, then fly high enough to ensure terrain clearance, then fly a triangular pattern with each leg of the triangle being 2 minutes long [...]

  • Is mentioned in this article about distress signal.

It seems limited to areas under radar coverage and may be redundant with squawking 7700 on the transponder.

What is the purpose and the procedure for declaring an emergency using a flight pattern. Is this an international code?

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Usually in the US for a towered field, you squawk 7600 for a communications loss and then watch for light-gun signals. For an un-towered field you just keep vigilant about traffic and enter the pattern to land. – Ron Beyer Mar 18 at 14:28
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I've never heard of it (and it isn't in the FAA's ATC orders) and it seems unlikely: how would ATC know that the aircraft isn't doing a training exercise or just flying in a triangle because the pilot feels like it? ATC might ask an aircraft to make turns to acknowledge instructions if the aircraft can receive but not transmit, perhaps that was what your informant was thinking about? See this question. – Pondlife Mar 18 at 14:45
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Flying in triangles as a distress signal is also mentioned as a plot point in Frederick Forsyth's delightful story The Shepherd (as told in audio every year by the CBC), in which a 1950s RAF pilot just wants to fly his de Havilland Vampire home for Christmas. – Zach Lipton Mar 18 at 16:52
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@Pondlife Well, assuming it's not common for pilots to fly triangles for fun or training, a reasonable procedure would be for ATC to just ask! If they don't get a response, radio failure is a good assumption. – David Richerby Mar 18 at 18:14
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@DavidRicherby That assumes the aircraft is already in contact with ATC, which may not be the case. It seems to me that this procedure would only be useful in a very limited case: VFR, on flight following (or otherwise in contact with ATC), in radar contact, within scrambling distance of aircraft that could help. If any of those things aren't applicable then either ATC will have no clue that help is needed or won't be able to do anything anyway. And why would a lost pilot waste time and fuel flying around in triangles rather than start navigating and/or looking for a good landing spot? – Pondlife Mar 18 at 18:42
up vote 22 down vote accepted

To my surprise, this does exist, at least in the UK. According to the Manual of Air Traffic Services:

7 Emergency Triangle Procedure

7.1 Pilots lost or uncertain of position and experiencing either transmitter or complete radio failure are advised, as a last resort, to carry out special procedures to indicate to controllers that they require assistance.

7.2 The aircraft fly at least two triangular patterns, before resuming course, as follows:

Table 1: enter image description here

7.3 If a triangular pattern is observed, controllers shall advise the D&D cell of the position and track and continue to plot the aircraft whilst it is within ATS surveillance system cover. Controllers should also be aware of the effect wind may have on the pilot’s ability to fly an accurate triangle.

I say "to my surprise" because there are well-established procedures for comms failure under IFR and under VFR. But having said that, it's possible that the triangle procedure is more useful in the UK (for example) than the US, where there are usually plenty of uncontrolled airports around and many pilots have no need to talk to ATC anyway. In the UK, with a much smaller airspace, fewer airports and more ATC control (at least, that's my understanding), it may be more critical to give even VFR aircraft a "last resort" to contact ATC.

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That does seem a little surprising. It does specify that the procedure is for if you are lost. If you are lost and have total com failure though I'm not sure what ATC can do for you anyway. – TomMcW Mar 18 at 18:14
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@TomMcW: Well they could send an interceptor. – Joshua Mar 18 at 18:27
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@Joshua, if the plane is flying right triangle, they will first try issuing vectors on the likely frequencies (frequency charted for the sector, last frequency the plane was heard on and 121.5). For one flying left triangle, or one that continues the right triangle after the vectors were issued, sending an escort fighter seems like the only option. – Jan Hudec Mar 18 at 18:40
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In the UK, the pilot would probably also be more likely to be close enough to controlled airspace that someone will care what pattern he's flying than in the U.S., where they could be a hundred miles or more from the nearest controlled airspace (below 18,000 ft., at least.) – reirab Mar 18 at 19:29
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I was also taught this during my VFR training in Australia, two clockwise triangles indicate you can receive but not transmit while two anti-clockwise triangles indicates you can't do either. It's only military, although I'm not really sure it would matter...you approach any controlled airspace without squawking or responding to radio contact and they're gonna figure out pretty quick that something's up. – Mark Feldman Mar 19 at 10:03

There is no standard pattern for an emergency(see Pondlife's answer), I suppose if you were really bored you could spell out "HELP" on somebodies radar scope, but if you are operating VFR in the US a controller really isn't going to notice that you are flying a triangular pattern. This would be dangerous though around airfields, since you want to remain in the standard pattern so you aren't confusing or surprising other pilots by coming in from odd angles. The best thing to do in this situation is to fly normally in a manner which other pilots can anticipate.

Squawking 7600 is the code for "Communications Failure" and this is the procedure I was taught for VFR (in the US), although it should hold for any ICAO airspace/field:

  • Set Transponder to 7600
  • Say intentions over the radio, the transmit may still work but the receive may be dead
  • Enter the traffic pattern with a standard pattern entry
  • Watch the tower for light-gun signals.
  • Acknowledge Signals by rocking wings or flashing landing/taxi lights.

For an un-towered field, you enter the pattern as normal and follow the traffic flow in to land, taking care to watch for other aircraft on a straight-in or other odd approach.

Class-B offers other issues, if you are outside of class-B and lose your radio you cannot enter the class-B airspace even squawking 7600. If you are already in class-B then you may be able to continue but personally if the aircraft is otherwise flyable I'd head for the nearest class-D or C. There may be some exceptions to this for IFR flight plans, but that should be spelled out in the information in the link below.

Here is a good read of the Radio Loss Procedures and exceptions to the ICAO standard procedures for different operational areas below it.

By the way, you should be flying with a current AFD, and using your cell-phone to contact the tower is a perfectly acceptable way of establishing communications.

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you cannot enter the class-B airspace even squawking 7600 I always thought the proper procedure was to squawk 7600, fly the last assigned heading/altitude then follow your flight plan. Does that not apply if your flight plan takes you into class B? – TomMcW Mar 18 at 18:06
    
I don't believe it does on a VFR flight plan, IFR may be different but since you are not technically under constant control by an ATC facility, you need to establish 2 way communications and have authorization to enter. If you can't get authorization, you can't enter. – Ron Beyer Mar 18 at 18:08
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That makes sense on vfr. ATC generally doesn't have your filght plan. On IFR it seems I've read on here numerous times that you simply do what is expected from your plan. I can't imagine they'd want you to stay out of class B because then you'd be off plan and they wouldn't know what to expect. – TomMcW Mar 18 at 18:11
    
I suppose if you were really bored you could spell out "HELP" or, if the wind is favorable, "Where Am I?". – mins Mar 20 at 9:17

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