Complexity of RNAV procedures

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It seems that it is a matter of when, rather than if, ground based navaids will be decommissioned. I was thinking about the feasibility of single-pilot IFR operations in a purely RNAV environment.

Take these two approaches:


The ILS/LOC approach has one remark, "ADF Required". The RNAV approach has 6 lines of remarks, in small text, plus two additional remarks in the plan view. Can a single pilot really be expected to read all of this text while hand-flying in IMC?

-- Joshua Levinson, March 9, 2010


That's an interesting point. The FAA probably has plenty of procedures for allowing people to add remarks, disclaimers, and other items to an approach plate... and no procedure for removing anything. So eventually all approach plates will have the same amount of text as a Tolstoy novella. The RNAV world, with its dozen or so types of equipment that might or might not be on board a particular aircraft, seems to be replete with special cases requiring a lot of text. I think that the Feds did set up the world of RNAV and RNP with a two-pilot crew in mind.

A lot of the extra text and complexity comes from the fact that the minimums are different depending on equipment type and local altimeter. In a world where human factors had been taken into consideration, you'd expect the GPS receiver to have the appropriate minimums in its database and display them for the pilot. You'd also expect to have the special case "I don't have the local altimeter setting" to be a menu option, with the GPS changing the minimum appropriately and listing the airports that were acceptable to use as alternative sources of altimeter setting.

But the FAA and industry seem to be incapable of thinking about small improvements like this. All of the effort goes into $200 billion changes such as "NextGen" that will never happen unless the U.S. economy starts growing like China's.

-- Philip Greenspun, March 10, 2010

I have never flown that particular approach, but it seems straight forward to me. The advantage of the RNAV approach is that the GPS will guide you through all of the waypoints on the approach and preload the missed procedures. You could hand fly this approach and the GPS unit will warn you of each upcoming turn and heading so it's not like a VOR based approach. I personally feel that it is easier to setup a GPS approach than ILS since you leave your CDI source on GPS the entire approach and just focus on the altitude step-downs. If you have WAAS and use the LPV approach you will also get the vertical guidance from the FAF in just like an ILS. ATC can make any approach more challenging, but you didn't mention that.

I routinely hand fly or sometimes just use the heading bug for GPS approaches and it seems a lot easier than many of the other types of approaches ie. VOR/DME arc. As an example on a dark night into an unknown field with terrain around the approach in IMC do you really trust your skills to do a DME arc approach or even a VOR circling approach vs. the accuracy and redundancy of the GPS system? For me it's ILS or GPS or fly to an airport that has them.

Phillip has said it before, "don't try to be better than an airline captain" and I don't.

-- Alex Baker, March 9, 2010

I agree, I wouldn't want to be better than an airline captain. An airline captain would be monitoring an autopilot while the first officer briefs the approach, reading all six lines of approach remarks to ensure that they really are authorized to fly that approach.

In a piston single with no autopilot, I wouldn't want to be taking my eyes off the instruments for the length of time it would take to read and parse all of those remarks, and figure out if I'm adequately equipped to fly that approach, all while hand-flying.

-- Joshua Levinson, March 9, 2010

Willingness to fly no autopilot single pilot IFR in my opinion is trying to be better than an airline pilot regardless of the approach type. I wouldn't do unless it is an emergency ie autopilot failure. Then I would rather have the GPS telling me turn in 5 seconds to heading X etc. than looking at the plate and tuning the VOR. In that circumstance I would also ask ATC for help with altitudes and headings given my autopilot failure.

Just my 2 cents.

-- Alex Baker, March 9, 2010

That's a fair point. Still, by flying single pilot at all, you're already starting at a place an airline captain wouldn't.

-- Joshua Levinson, March 9, 2010