Tuesday, December 22, 2009

Starting off on the wrong foot


I'm confident that I will fly again, so I've started to review. Instrument flying really demands review, because the regulations are complex and changes happen quickly. (I've written about this before; see this post or this one.)

I found something interesting right away: a new departure procedure for Pocatello, pictured above. It's called the
KNURL ONE (OBSTACLE) departure.

A great way to improve your understanding of IFR flight, as well as your chart-reading skills, is to spend a lot of time asking "Why?" Why is there a new departure? Why does it use that radial? Why does it use that altitude? And the like.

The FAA uses two classes of departure procedure, SIDs (Standard Instrument Departures) and ODPs (Obstacle Departure Procedures). Wait, isn't the term SID deprecated? No; now it is undeprecated, or is that repricated, or maybe vindicated? Whatever you want to call it, see the preamble to the TAKEOFF MINIMUMS AND (OBSTACLE) DEPARTURE PROCEDURES section of any approach chart book. SIDs are back.

The first thing to notice is that it is an Obstacle Departure Procedure. The obvious clue is the word (OBSTACLE) in the procedure title, but there's a subtler clue as well, which is easy to miss because it is often, well, missing. SIDs generally do not include altitudes, and many that include altitudes use the notation (ATC) to indicate that the reason for the altitude restriction is for the convenience of Air Traffic Control; see for example the WHAMY ONE departure out of Portland, Oregon. You also see this with climb gradients, when ATC wants you to climb like crazy to get above the inbound traffic.

With IFR procedures the first consideration is altitude, so if you don't see one there's a reason. And ODPs, because of their nature, always include lots of altitudes. So, in the KNURL departure from runway 3, you read "Climb heading 028 to 5500, then..." That's to get you over the grain elevator.

After maneuvering away from the obstacles, the departure has you fly outbound on the PIH R-269 to KNURL, which is at 17DME. Ouch! That's a long way in a 172 or even an Archer, but it makes sense if you are headed west on V-500, which uses R-269. But that makes no sense in a 172 or Archer, since the MEA on V-500 between REAPS and DERSO is 17,000 MSL!

ODPs are optional and may be flown without a clearance, although I would consider it good form to inform ATC if you decide to fly it. So why would you follow an optional departure procedure that takes you down the radial you want to fly?

Worse, the ODP altitude is 7,500MSL. This leaves higher altitudes available for ATC, which is good. But it has you flying westbound at an eastbound VFR altitude, which would make me very uncomfortable on a marginal VFR day. If I had the equipment to get to 17,000 I would rather file for that altitude (or even higher) rather than fly head-to-head with the VFRs, nice folks though they are, down low.


Now let's look at how this DP fits with the enroute structure. There are six airways at Pocatello VOR, and because of terrain most departures are on one. Starting at north, V-21 goes northeast to Idaho Falls. Pocatello departures are unlikely to fly 17 miles west before turning northeast, especially since there is nothing to hit in that direction. Departing runway 21? Turning right at 400AGL will put you on the 016 radial? Departing runway 3? Just turn a little to the left. (Virtually no aircraft depart runways 17 or 35 except under extreme conditions, which would require some careful thought.)

The next airway is V-21 southeast bound. There is a crossing restriction at the VOR, so maybe a little jaunt down the 269 radial would be comforting. But all the way to KNURL? Plus, if you are on the ODP you are restricted to 7500, and the crossing altitude is 8000.

V-269 southeastbound follows the 235 radial, and the MEA is lower. If you're going that way, just fly V-269.

We've already discussed V-500.

V-269 northbound goes toward Salmon (LKT) over relatively low terrain for the first 50 miles. You are perfectly safe just turning to intercept, except perhaps departing runway 17. The same applies to V-257, toward DBS.

The other departure direction is toward Jackson Hole, WY. The heading is about 045, so one might be tempted to make a left turn departing runway 21, but that throws you toward high terrain. I always flew the right downwind departure, passing over the airport.

The conclusion?

Nobody will ever request the KNURL ODP!

It is still possible that ATC will assign the departure in order to get an airplane moving. Shoot the departure to 7500, keep the inbound at 9000, and everybody is happy. Once the departure is in radar contact they can vector it to where it wants to go. And if there's lost comm? Well, the departure is stuck down at 7500 for 10 minutes.

Still, you would interpret that as starting off on the wrong foot.

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3 Comments:

At December 29, 2009 at 8:51 PM , Blogger Andrew said...

Hey Dr.

read your comment on Ian's blog and thought i'd come check it out, looks like i've got a lot of reading ahead of me, Great Blog...

Andrew

 
At December 29, 2009 at 8:56 PM , Blogger Andrew said...

Its me again...is there anyway i can follow your blog?

 
At April 2, 2010 at 4:56 PM , Blogger Dr.ATP said...

I recently found out that SkyWest is using the KNURL departure; their Op Specs probably require them to use any available Obstacle Departure Procedure. It looks like ATC turns them to the southeast long before they get to KNURL, though.

 

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