Pop-up IFR clearances are an accepted way to transition from VFR to IFR flight by obtaining an IFR clearance. They are well documented from a controller's perspective in this Tarrance Kramer article appearing in AvWeb and from a pilot's perspective in this Rick Durdan article appearing in AvWeb.
These related Aviation.SE questions also address the topic:
- How do you request a “pop up” IFR clearance?
- How do you open and get a IFR clearance while in the air?
- How should I request an IFR approach at the end of a VFR flight?
Clearly, this is an accepted way to obtain an IFR clearance; I have made use of the option myself plenty of times.
Now, pop-up clearances are often requested and granted with no previously filed IFR flight plan which, on the face of it, would seem to be in violation of 14 CFR 91.173 which states (emphasis mine):
No person may operate an aircraft in controlled airspace under IFR unless that person has—
(a) Filed an IFR flight plan; and
(b) Received an appropriate ATC clearance.
14 CFR 91.169 gives the information required for filing that required IFR flight plan, which states, in part (emphasis mine):
Unless otherwise authorized by ATC, each person filing an IFR flight plan must include in it the following information: [...]
(I omit the long list of actual information)
The first part of my question is:
Does a request for a pop-up IFR clearance constitute filing a flight plan?
Is there an unwritten (or perhaps written) understanding that the request for the IFR clearance constitutes filing a flight plan to the extent required by 14 CFR 91.173?
The second part of my question is:
Why is the full list of information required for filing an IFR flight plan not required, in fact, of a pilot requesting a pop-up IFR clearance?
If ATC issues an IFR clearance without this information, is that a tacit, but legally valid, authorization to exclude the information otherwise required by 14 CFR 91.169?
Is all this actually codified somewhere that I am not aware of?