Originally posted by Wolfala
OK iron man - what happens when your ground speed goes from the 110 knots that you are used working at, to 170 with a tail wind heading south and ATC switches an intersection to some off airway fix...
If you know how to get to the off-airway fix, you just fly there. Headwind switching to tailwind is a simple correction as long as you understand ratios and the 60/1 rule, or have good rules of thumb that don't break down when you are outside normal cruise or approach speeds. If you can't get there (or in situations I've been in, where the fix is some obscure point not on any of my charts and not in either the approach or departure books) you reply "unable" and ask for an alternate clearance. If they are unwilling or unable to provide a clearance you can comply with, you do one of two things.
1. Cancel and proceed VFR
2. Declare an emergency, do whatever you feel like doing, and let the uptight controller deal with your sudden elevation in priority. And hope the FAA guy who comes out to interview you is understanding.
In the last 13 years, I've only had to twist the controller's arm about 3 times. One time, they were unwilling to clear me out of icing conditions. I was about 10 seconds from squawking emergency when they finally realized I was serious about not crashing that day and cleared me to climb out of the thin but ice-filled cloud deck they'd parked me in. Another time, I arrived during "rush hour" about 5 min ahead of my expected arrival slot, and the controller assigned me a penalty hold that would have taken me about 15 minutes beyond my expected arrival time. I didn't have 20 min of fuel to spare so I came back "unable". The controller fitted me into the arrival flow like a champ and didn't even complain about it. He was even gracious when he accidentally put me 1500 ft above glideslope at the FAF at night, after telling me to maintain max speed due to a 737 next in line. I made it work through some creative application of aerodynamic theory, and he thanked me for not going missed approach and making him have to fit me in a second time.
This one was more entertaining... I was #2 in a 7-ship string of tweets heading to florida, all instructor training so we had 14 IPs and no students. The first guy was cleared to some fix, and being the good IP I am, I immediately started looking for it too since I knew I'd get the same clearance in just a few minutes. The guy ahead of us gave sort of a "uhh yea cleared to whateverrequestinitialvectork
thxbye" answer, so I knew he didn't know where the heck the fix was. I figured I had 5 min to find the fix. Well, I pulled out every book and chart we had in the plane, and couldn't find it. They gave us the same clearance plus a helpful initial vector, but I still couldn't find the fix. Not being willing to play stevie wonder with the approach, I told them I was unable to proceed on that clearance, and asked for something a caveman driving a wright flyer could do. The clue light clicked on at rapcon since this sort of thing happens anytime a VOR/ILS/DME only jet shows up (ie. a T-37), and the controller gave me something easy (direct to a VOR/DME IAF if I recall correctly). The guy ahead of me immediately piped up with "uh yea we're also... uh... unable... request uh....", and he got the same amended clearance. The guy behind me heard all this going on, and admitted defeat early. By now, the controller figured it out and the rest of the gaggle all ended up with an approach flow that was actually in our approach books.
To this day I still don't know where the heck that point was, but it may have been a fix on a SID, or a GPS or RNAV coord point. Why they'd use a point published only in a departure procedure to handle arrival flow, I don't know. But I do know that of the 14 IPs on that flight, not one of us were able to comply with the clearance.
The moral of the story of course is to know the capabilities of your system and to not hesitate to come back with "unable" if either your system is not capable of the navigation task, or if you are personally unable to comply. Either reason is perfectly valid, although if you routinely come back with "unable" for anything but vectors to final, sooner or later you're gonna piss off a controller and have a nice long chat with an FAA examiner.
