A Point-to-Point through the FARs

[HokiePilot]

I used PTP all the time in the fleet. But it was always during SSC. "There is a contact at mom's 215 for 15. Can you check it out? " Type thing. The pilot in the left seat would normally plot it out and drop a fly-to-point, but you should be able to make the initial turn within 15 degrees.

IFR PTP? Yeah, I never did that.

Oh, and there was a Mishap 2004 time frame where a -60B crashed after some sort of heading gyro malfunction. I forget the exact details.

 

[HokiePilot]

And my theory on partial panel when I was an instructor in the HTs centered on that aircraft. Students should be competent enough to mitigate the risk on their solo. IUTs more so because it is much more likely to happen with one of them in the aircraft.

We had an instructor have a heading gyro malfunction in IMC while I was there. She had to shoot an ILS to 200 feet with that. I always had IUTs read that HAZREP during the brief for the failed card flight.

 

[Brett327]

I guess I don't know what I don't know.....but if you told me to fly to that fix I could probably hit it within a couple of miles without even trying very hard. What is the actual tolerance when cleared to a fix?

Granted, I'm using an HSI so it's a little easier...but illegal?

Even easier now (soon) with sticky rubber band in H14, assuming you're in an HOL/ACS jet.

 

[wlawr005]

So the range bearing tool stays now?

 

[Brett327]

You can stick each end to a point in space/PPLI/other contact and get your cursor back as it continues to update range/bearing. Pretty useful.

 

[FinkUFreaky]

Similarly, in the E-2 (C at least) community PTPs were used literally every night trap to get to marshall. Granted we had some help and could theoretically plot a spot that is "close" but a good true PTP was generally better in my estimation (but I don't hate airborne math-related caculations, a lot of people truly do). Maybe something that doesn't need to be taught at primary anymore though... Maybe teach it in communities that need it. Or use it as a weeding out tool. I know that I do not know what is best.

 

[FinkUFreaky]

On a similar note I do think it's funny how much training we spend on holding WITHOUT the timing element (being ready to push within +-10 seconds from a spot that is always moving). Realistically you will likely never be told to hold (myself, not a single time except when requested) unless severe conditions exist if you aren't going to the boat. And until the fleet, you won't be flying in severe weather conditions. Yet you hold every single time at night carrier ops. So maybe not put quite as much of an emphasis on it in primary? Like the different type of entries, etc that the FAA doesn't give a shit about.. Maybe just that they care what side we end up on, and if they go in a community where it matters they train them on that other stuff there? Maybe experience it at least once airborne (like airborne change of flight plans)? I still realize there's likely a reason it is the way it is. Just throwing out ideas.

 

[RobLyman]

You're following. The argument is that when flying a radial, you can measure how far off that radial (or GPS course line) that you are (ie, XTK) by the deflection of a CDI (or GPS CDI/XTK distance). But when you moving from one point in space to another point in space with just a VOR/DME or TACAN, you're not able to measure any deviation from the initial required course because there is no way to depict the course line. Essentially, as the argument goes, you're homing, not navigating.

Like many things that are different between the services, I think it's a matter of comfort level. Apparently the FAA is no longer as comfortable with it either.

14 CFR 91.177 - Minimum altitudes for IFR operations. (ii) In any other case, an altitude of 1,000 feet above the highest obstacle within a horizontal distance of 4 nautical miles from the course to be flown...
You can, and probably have, looked up the rest of the stipulations.

When flying point-to-point if you can't maintain some degree of accuracy (cross track error), then you can't be guaranteed obstacle clearance or aircraft separation requirements have been met. For a jet at altitude, "within a few miles" might be fine. For a helicopter already flying at minimum altitudes, 1/2 mile of deviation might get you too close to an obstacle. Do VFR flight following near some tall towers and see if ATC doesn't require you to fly around them (ie vector you) unless you have visual contact.

Tbl 1-2-1 in the AIM shows required navigational performance (RNP) required for different phases of flight. Enroute is 2 NM from centerline. Terminal is 1 NM and approach is .3 to 1 NM. Also from the AIM, "For an aircraft to meet the requirements of RNAV, a specified RNAV accuracy must be met 95 percent of the flight time." (Sorry for the AIM vs FAR reference. I don't have my tabbed out and highlight FAR/AIM with me. The AIM is easier to search.)

You can see that poor execution of TACAN point to point probably does not fulfill RNP requirements, especially in the terminal and approach arena.

 

[Brett327]

Hazards of navigating a helo at low altitudes notwithstanding, my understanding of RNP is as a metric of GPS system accuracy required to legally use RNAV in any given phase of flight, not a metric of accuracy of what the FAA expects you to fly, particularly if doing a TACAN PTP. We may be splitting hairs here, but I just want to make sure my understanding is accurate.

 

[bucka]

Amateur question: if I can put a TACAN offset into the T-45 and get a distance, course, and CDI to my radial/dme cut, does that count as an RNAV function? Sounds like it does, as the system provides cross-track error.

 

[sevenhelmet]

14 CFR 91.177 - Minimum altitudes for IFR operations. (ii) In any other case, an altitude of 1,000 feet above the highest obstacle within a horizontal distance of 4 nautical miles from the course to be flown...
You can, and probably have, looked up the rest of the stipulations.

When flying point-to-point if you can't maintain some degree of accuracy (cross track error), then you can't be guaranteed obstacle clearance or aircraft separation requirements have been met. For a jet at altitude, "within a few miles" might be fine. For a helicopter already flying at minimum altitudes, 1/2 mile of deviation might get you too close to an obstacle. Do VFR flight following near some tall towers and see if ATC doesn't require you to fly around them (ie vector you) unless you have visual contact.

Tbl 1-2-1 in the AIM shows required navigational performance (RNP) required for different phases of flight. Enroute is 2 NM from centerline. Terminal is 1 NM and approach is .3 to 1 NM. Also from the AIM, "For an aircraft to meet the requirements of RNAV, a specified RNAV accuracy must be met 95 percent of the flight time." (Sorry for the AIM vs FAR reference. I don't have my tabbed out and highlight FAR/AIM with me. The AIM is easier to search.)

You can see that poor execution of TACAN point to point probably does not fulfill RNP requirements, especially in the terminal and approach arena.

The table you reference is in a section of the AIM (1-2-2) which specifically defines RNP as RNAV with onboard navigation monitoring and alerting, and thus is not applicable to TACAN/VOR navigation.

TACAN/VOR generally gets more precise as you get closer to the station (the "cone of confusion" at high altitude nonwithstanding), which is what enables it to be used for non-precision approaches. Many of those approaches require PTPs to reach the IAF, and a proper understanding of geometry and aircraft turn performance in order to arc and turn to radials. So yes, poor execution would be an issue- but you could argue the same for a poorly hand-flown RNAV approach. Bad piloting is bad piloting, regardless of the nav source.

 

[wlawr005]

I was thinking the same thing. RNP isn't really applicable to TACAN flying.

 

[scoolbubba]

On a similar note I do think it's funny how much training we spend on holding WITHOUT the timing element (being ready to push within +-10 seconds from a spot that is always moving). Realistically you will likely never be told to hold (myself, not a single time except when requested) unless severe conditions exist if you aren't going to the boat. And until the fleet, you won't be flying in severe weather conditions. Yet you hold every single time at night carrier ops. So maybe not put quite as much of an emphasis on it in primary? Like the different type of entries, etc that the FAA doesn't give a shit about.. Maybe just that they care what side we end up on, and if they go in a community where it matters they train them on that other stuff there? Maybe experience it at least once airborne (like airborne change of flight plans)? I still realize there's likely a reason it is the way it is. Just throwing out ideas.

While not 'useful' in the age of GPS and the magenta line, the PTP and Holding are fundamentals of flying radio instruments. Much like learning a language, you don't start speaking and writing at the doctoral level and then go back and learn how to conjugate verbs. The PTP is the execution piece of understanding how to read an HSI/RMI, envision where you are oriented (or is it orientated for my green brothers?), and WAG a course to a new point in space relative to the station while making adjustments along the way.

Am I doing that in a 737? No. Could I if I needed to? Yep.

Same with holding. It is a tough concept to wrap your head around in the early stages, which is primarily why we put so much emphasis on it. You get the reps at it that you need in primary so that it becomes second nature early on. Emphasizing the proper entry is a way to judge if the student actually understands where they are in relation to the fix and how they plan to enter the hold. In reality, do I give a shit as long as I end up on the protected side? Nope. And i don't know why timing wasn't emphasized in the hold for you; it should have been. I don't like that the procedures are written to require two full turns before you start working to correct the timing, but it's definitely an emphasized point in holding to make adjustments to hit the fix on time.

In 30 years when every ground based navaid is gone, sure, we can do away with these kind of procedures. 2 minutes later, when GPS gets turned off because we forgot to pay the bill or pissed off the chinese, we can just go back to using compasses and watches for everything.

 

[FinkUFreaky]

While not 'useful' in the age of GPS and the magenta line, the PTP and Holding are fundamentals of flying radio instruments. Much like learning a language, you don't start speaking and writing at the doctoral level and then go back and learn how to conjugate verbs. The PTP is the execution piece of understanding how to read an HSI/RMI, envision where you are oriented (or is it orientated for my green brothers?), and WAG a course to a new point in space relative to the station while making adjustments along the way.

Am I doing that in a 737? No. Could I if I needed to? Yep.

Same with holding. It is a tough concept to wrap your head around in the early stages, which is primarily why we put so much emphasis on it. You get the reps at it that you need in primary so that it becomes second nature early on. Emphasizing the proper entry is a way to judge if the student actually understands where they are in relation to the fix and how they plan to enter the hold. In reality, do I give a shit as long as I end up on the protected side? Nope. And i don't know why timing wasn't emphasized in the hold for you; it should have been. I don't like that the procedures are written to require two full turns before you start working to correct the timing, but it's definitely an emphasized point in holding to make adjustments to hit the fix on time.

In 30 years when every ground based navaid is gone, sure, we can do away with these kind of procedures. 2 minutes later, when GPS gets turned off because we forgot to pay the bill or pissed off the chinese, we can just go back to using compasses and watches for everything.

Good points. I wasn't clear on the timing portion, I get that we emphasize one minute legs, etc. I meant the "hit the point at this exact time" timing.

 

[Jim123]

Good points. I wasn't clear on the timing portion, I get that we emphasize one minute legs, etc. I meant the "hit the point at this exact time" timing.

Hitting consistent legs (while doing a bit of math and flying the plane) is a building block to hitting a holding point at +/- 10 seconds.

Most primary IPs aren't too hung up on nailing the angle and timing corrections to a gnat's ass. Most are looking for SA of the wind, do I have to crab left or right, do I have to add or subtract outbound time, and is it a big correction or a little correction. Some students fly around the racetrack a few times, in awkward silence and without verbalizing what they think the correction should be. My attitude was I know that guys' basic airwork is rarely perfect and the wind sometimes changes, but until you say what's on your mind then I can't grade the maneuver...

There's probably venn diagram of the student world and the instructor world and the areas don't overlap as much as they should when it comes to holding.

Getting the entry orbit right is something we make harder than it has to be. The Air Force has taught the "God's eye view" of figuring out the entry for a long time- basically you draw the entry with your finger on a map. Amazing. I think that is a lot easier than the "use your hands to make gang signs 70/110/180 right/left of the reciprocal of the inbound course and WTF does that even mean" method in the Navy pubs.

Might as well train people to use the most efficient entry method while being oriented- it'll make everybody's lives easier later when they have to hold in a marshall, refueling track, CAS stack, whatever else- or fly a windline rescue pattern (a not entirely different procedure).