But let a cloud layer thicken, an undercast rise, storm cells form, or your destination’s ceiling or visibility head downhill, and continuing VFR can go off the table. But as an instrument pilot, you have an option.
You can “air file,” or file an IFR flight plan while en route. Ideally, this would involve calling up the nearest ATC frequency, stating your N number, and waiting for a controller to acknowledge your transmission. When that comes, go ahead and give a position report of sorts, stating that you’re VFR, giving your position and altitude, and adding “request” to your transmission. “Go ahead with your request,” will hopefully be the answer, and now you can tell the controller you’d like to file an IFR flight plan to your destination. But don’t get your hopes up.
One good strategy for quicker air filing is to establish contact with ATC, then request flight following (VFR advisories). Again, this service is given on a workload-permitting basis so there are no guarantees. But once ATC grants flight following, you’ll be spring-loaded to air file. ATC already has you identified, knows your altitude, and has been keeping track of your flight. ATC is more prepared than if you cold-called them.
So, ATC can, and does, file IFR flight plans on the fly, but it depends on the circumstances. These sorts of “pop-up” clearances are granted on a workload-permitting basis. Congested airspace and changing weather conditions may keep controllers so busy that they can’t easily take a time out from their existing duties to make room for copying your flight plan, entering it into the system, and issuing you your clearance. But if you’re far from dense traffic and assuming the fates are with you, the controller might come back with “go ahead with your flight plan.”
At this point you can go ahead with the flight plan sequence, stating the elements in the order they appear on the (non-ICAO, thankfully) flight plan form. After it’s acknowledged and you’re issued your clearance, you’re in the system. Congratulations, you lucked out this time. However, the awful truth is that the FAA would rather you not air file with ATC, except in extenuating circumstances, and take care of your flight plan filing using other means. (Of course, in an emergency you’re free to contact ATC or perform any other procedures you deem necessary to deal with the emergency and ensure the safe continuation of the flight—even if it means violating the FARs. This is covered in FAR 91.3.)
Ironically, one of those other means of IFR flight plan filing is…air filing. But using a flight service station’s advisory frequency, not ATC frequencies. These can be found on IFR low-altitude en route and VFR sectional charts. They’re published right above most of the boxes that enclose VOR identification, Morse code, and latitude/longitude information. On high-altitude IFR charts the information within the box is abbreviated, but the FSS frequency still appears above the box. The name of the nearest associated FSS in typically enclosed in brackets, beneath the VOR’s identification box. All that’s for government charts. Jeppesen charts use different conventions—like putting the FSS frequencies within the navaid identification box.
The most common FSS frequencies are 122.2, 122.4, and 122.6 MHz. Your callup should use the same standard mentioned earlier, only using the name of the nearest designated FSS. For example, you’d use “Saint Louis Radio” when near the Farmington, Missouri, VOR, because “Saint Louis” is in the brackets below the Farmington VOR’s identification box. Once communications are established, you dictate your flight plan, FSS copies it, sends it along to ATC, and gives you an ATC frequency to contact for activation and clearances.
While you’re at it, you might also obtain an FSS weather briefing for your route of flight. This can be a full-blown standard briefing or an abbreviated version, your choice. Because you have the luxury of time when talking over an FSS frequency, you can get a deeper dive into descriptions of convective and other weather that could affect the rest of your flight.
Sometimes you might see 122.1 MHz posted above the VOR identification box, along with the letter “R.” This means that FSS can receive you over 122.1 MHz. So, you broadcast on 122.1. To listen to FSS, you’ll have to dial up the volume and set up your com radio so you can listen to the VOR frequency. This is where FSS transmits to you. So, your com radio is tuned to 122.1 and your nav radio is tuned to the VOR frequency, with the ID or Voice function selected. Welcome to old-school procedures, held over from those times where transmitting and receiving on the same frequency weren’t possible when cruise altitudes were comparatively low, and distances from the station may have been too great.
For the callup on this split-frequency arrangement, you have to tell FSS the frequencies you’re using for transmitting and receiving. To use the Farmington VOR example, you’d say “Saint Louis radio, N12345, transmitting 122.1, listening Farmington VOR.”
After that, it can get a little chaotic. Other pilots may also be transmitting on 122.1, and you’ll hear the VOR’s Morse code behind the FSS briefer’s transmissions. It can get confusing. You may have to ask the briefer to “say again please.”
Are there any other ways to air file? If you have the systems—and can swing it financially—you could use a satellite phone to call an FSS for an in-person brief-and-file session. But this option seems to be only for high-rollers flying big iron.
If all this sounds like a hassle, you can always fall back on filing your flight plan after the preflight briefing, and flying IFR from takeoff to touchdown. This can be done the old-fashioned way over the telephone with flight service, or using the flight plan functions on tablets running ForeFlight, Garmin Pilot, or other apps. After that, you’d pick up your clearance from clearance delivery at bigger airports, from ground control or tower at others, or right before takeoff if you’ve been issued a void time. If the void time expires before you take off, your clearance expires, and you have to file all over again. Facing a frustration like that can make air filing an appealing process.