Is there any FAA guidance which specifies when a call sign & flight number or registration number must be used for Part 91 & 135 operations?

I am familiar with the guidance on how to obtain an ICAO call sign (and in fact work for a company who has one), but am unable to find anything which specifies when one must be used versus the other.

So basically, can commercial flights file under the registration number and can private flights (re-positioning flights, etc.) file under the company call sign? I understand that this is backwards from "typical" use, but is it legal?

  • $\begingroup$ Related, although it doesn't address the part about filing $\endgroup$
    – Pondlife
    Commented May 11, 2016 at 16:42
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    $\begingroup$ FAA AIM Section 4-2-4 has guidance on using call signs and registrations in certain situations. $\endgroup$
    – Ron Beyer
    Commented May 11, 2016 at 17:15
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    $\begingroup$ @Lnafziger Subsections 3, 4, and 5 don't clear that up for you about civil aircraft, air taxi, and air carriers? $\endgroup$
    – Ron Beyer
    Commented May 11, 2016 at 17:20
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    $\begingroup$ It might fall under the "if you have a call-sign, use it", the only other document I can find that talks about when to use call signs is JO 7110.65W ATC Operations Section 2-4-20 which basically just reiterates what is in the AIM. "2. Air carrier and other civil aircraft having FAA authorized call signs. State the call sign followed by the flight number in group form." Doesn't seem to matter if its a positioning flight, if it has an ICAO call sign, it should be used. $\endgroup$
    – Ron Beyer
    Commented May 11, 2016 at 17:37
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    $\begingroup$ @RonBeyer Part of what prompted this question is that I am conducting an internal evaluation checklist provided to us by a major safety organization, and one of the questions is to verify that "commercial flights are always conducted under a flight number, and private operations (e.g. repositioning flights) are always conducted under the aircraft registration number." They reference Order 8900.1 as the regulatory requirement, but I can't find anything to back up the supposed "requirement". $\endgroup$
    – Lnafziger
    Commented May 11, 2016 at 18:59

1 Answer 1


I found something relevant buried in the depths of JO 7340.2 on contractions (i.e. abbreviations) for airlines, aircraft types etc. Section 1-4-2 says:

The company designator, together with a flight number, serves as the aircraft identification in the ATC system. Company designators are valid only for company business in accordance with the provisions of its operating certificate or servicing organization. Pilots will use standard identification procedures for personal flying

Compare that to the quote from your safety organization:

commercial flights are always conducted under a flight number, and private operations (e.g. repositioning flights) are always conducted under the aircraft registration number.

If you remove the words "e.g. repositioning flights" then it's saying almost exactly the same thing. What's really odd is that the checklist uses repositioning as an example of a "private operation" (the JO uses the words "personal flying", which has different connotations). I think most people would say repositioning is definitely company business. Perhaps it's just sloppy wording or a poorly chosen example.

As for the safety organization's claim that there are specific requirements in 8900.1, I couldn't find anything. The only vaguely similar thing I found is the 'use it or lose it' clause in 2-275:

B. Failure to Use Three-Letter Company Designator and Telephony Designator. ATO AJV-2 will place on a watch list any company that does not use an assigned three-letter company designator and telephony designator for 2 years on an instrument flight rules (IFR) flight plan in U.S.-controlled airspace. ATO AJV-2 will revoke and release any three-letter company designator and telephony designator that are not used for 3 years on an IFR flight plan in U.S.-controlled airspace.

Whoever wrote your checklist might be saying that you need to make sure that you're using your company call sign regularly to make sure you don't have it revoked, but that seems like a real stretch to me. And even if that is the case, it wouldn't explain why repositioning flights should be different. Since 8900.1 is a very large reference library, I'd ask the safety guys to point you to the exact document and wording.

Looking in the other usual sources (FARs, AIM, P/CG, ATC orders etc.) that you and Ron mentioned, I couldn't find any specific legal or regulatory requirements either. Almost every reference in FAA sources says "registration or call sign" or something similar (e.g. the AIM's instructions on filing flight plans), and the FCC regulations allow either in radio use (47 CFR 87.107).

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    $\begingroup$ Thanks for the research! It does look like a wording/intent difference, as people casually use different terms to mean the same thing when they actually have different legal meanings (commercial/company business/part 135 (or 121 as appropriate) ). Where it was fuzzy is when a flight is something like a non-commercial, part 91 repositioning flight, for company business, lol. I was hoping for a letter of interpretation or something that was more specific, but this is a good find! $\endgroup$
    – Lnafziger
    Commented May 16, 2016 at 15:49

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