Northwest 188 -- Clearance Limit

Who has thought of it ? Have you ? In all the writing about NWA188 -- in all the stories -- has anybody said a single thing about their clearance limit and the implications of it ?

”CLEARANCE LIMIT - The fix, point, or location to which an aircraft is cleared when issued an air traffic clearance .“

The clearance limit of NWA188 was the MSP airport -- and no further.

From the controller’s “bible” -- the FAA 7110.65:

10-4-4. COMMUNICATIONS FAILURE

”Take the following actions, as appropriate, if two-way radio communications are lost with an aircraft:

NOTE-
1. When an IFR aircraft experiences two-way radio communications failure, air traffic control is based on anticipated pilot actions. Pilot procedures and recommended practices are set forth in the AIM, CFRs, and pertinent military regulations.“

The pertinent “CFRs” -- Code of Federal Regulations -- are in section 91.185. Here’s the “legaleze” for those that demand such things:

§91.185 IFR operations: Two-way radio communications failure.

”(a) General. Unless otherwise authorized by ATC, each pilot who has two-way radio communications failure when operating under IFR shall comply with the rules of this section.

(1) Route. (i) By the route assigned in the last ATC clearance received;

(3) Leave clearance limit. (i) When the clearance limit is a fix from which an approach begins, commence descent or descent and approach as close as possible to the estimated time of arrival as calculated from the filed or amended (with ATC) estimated time en route.

(ii) If the clearance limit is not a fix from which an approach begins, leave
the clearance limit at the expect-further-clearance time if one has been received, or if none has been received, upon arrival over the clearance limit, and proceed to a fix from which an approach begins and commence descent or descent and approach as close as possible to the estimated time of arrival as calculated from the filed or amended (with ATC) estimated time en route.”

Switching back to English, the pilots had two routes to choose from when they reached their clearance limit (which, again, was the MSP airport):

1) Commence descent and approach

2) Leave the clearance limit and proceed to a fix from which an approach begins.

Now...clear your mind of legal stuff and let’s think of safety. The controllers need some assumptions to base their actions on. “The Book” says to assume the pilots will commence an approach (a defined Instrument Approach Procedure to the airport) or proceed to a point from which an approach can be made (an Initial Approach Fix.) Why should the controllers assume the computer programers programmed the autopilot to do anything different ?

You thought of this, right ? You thought about the implications of all this didn’t you ? It’s an autopilot, right ? Shouldn’t “Auto” be programmed to do the same thing that Tim, Dick and Harry are expected to do ? If the FAA is going to bust the pilots for not doing what they are supposed to do, is the FAA going to go bust the programmer for programming the autopilot to do whatever it did ?

I don’t know what the autopilot was programmed to do (that’s sort of the point) but it wasn’t what “The Book” said to do now was it ? And if we’re not going to do what “The Book” says to do then why have “The Book” ? Shouldn’t the folks that program the computers know what “The Book” says so they’ll know how to program the computers ? If we’re going to have programmers substituting their actions for a pilot’s actions shouldn’t they have an understanding of the consequences of those actions ? And shouldn’t they be accountable for those actions ?

And while you’re struggling to answer those questions within the framework of your gee-ain’t-technology-cool context, riddle me this; Who (in the FAA) certified all this ? Seriously. When the programmers said, “If the autopilot reaches it’s clearance limit it will default to flying present heading.”, who in the FAA said, “Okay, that’s approved.” ?

I could go on. This isn't the only who-certified-this-computer-programming-logic question I have. Would you like to talk about flying airways with a GPS in non-radar airspace ? “Say distance from Sugarloaf VOR...the VOR behind you.” Yeah, I didn’t think you wanted to talk about that either.

Don Brown
December 13, 2009

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