Moonwolf

yes it’s a stupid question.

cencal83406

I would think the Boeing with the loss of NAV would go into CWS R (yellow box) and maintain the roughly last action the aircraft was doing.

in 75 it should cross through LNAV and operate in a attitude stabilizing mode.

not sure I’ve seen a 73, 75, 76 go to heading select when the LNAV degrades for one reason or another.

I’ve seen the heading bug in the direction of the ETOPS airport because heading isn’t the first thing you do on a track divert anyway… typically you stay in LNAV the whole time since the procedure is to offset with it to begin the process of vacating the track system. So you’d offset, descend before 29, do drift down speed, then decide where you’re going - at that point you could refine the heading but for direct but seems like it’d be just as fast to add a new destination then select it to L1 on the legs page execute then off you go (direction of the turn below the tracks not factored in this quick though).

7321

Your right. It does go into CWS. I had LNAV fail a few months ago. Plane went CWS R exactly as you describe. Got LNAV back immediately - stray electron I guess.

Smooth at FL450

all of this sounds like making easy hard.

7321

I agree. Just looking for info.

zippinbye

I can tell you one genesis of this technique, nothing to do with Hawaiian. At a certain red-tailed airline, back in the pre-GPS Dark Ages, we used this thing called triple INS naviagation for RNAV and overwater naviagation. The most utilized units were Universal and Litton. I only used Litton, which was pretty fancy due to having a robust capacity for waypoints. Wheras Universal was very limited. I want to say maybe 7 waypoints? No more than a dozen as I recall. It was so constrained that future waypoints needed to be typed in as the most recent fix was sequenced. So if you were a slacker crew and failed to keep updating, guess what happened when the last waypoint was sequenced? That's right, revert to "Heading" with no aural or other obvious caution. The reversion might have been different on Boeing vs. Douglas, but the practice of slewing the bug toward a potential divert was pervasive throughout fleets. Uncaging the bank limit was part of it too. Experience an unexpected large banking turn? Check your FMA, INS legs, etc. It stuck for years after the suseptible INS units were in the bone yard. So I'm guessing the heading bug virus migrated across the ramp in HNL at some point, and now you guys are stuck with it! It took a merger for us to be whipped into shape. History repeating itself?

The real fun was making landfall and getting a position update based on the first VORs received. Position "accuracy" was measured on whole miles - no use for tenths. 2 was okay and finding an island counted as a "pass." I say that somewhat in jest, but by today's standard's, it was sketchy.

7321

Thank you! This historical information is great for perspective. On our 737's we are trained to slave the heading to current heading while in LNAV. It is so prolific that some people do it so much it is almost nauseating watching them do it - until I say, "please stop". When our 737 guru retired I asked him why pilots are taught this technique - he said there was a reason 30 years ago but not anymore.

Yep, I like your term, "virus", as that is exactly what it is. Your perspective and answer was exactly what I was looking for zippinbye. Thank you!

I put the HDG BUG to the right for this reason on ETOPS. If I get a big bank I will know why. It was a technique I was told HAL used but maybe it was, "red-tail " that did it. A Check Airman I had in the seat was OK with it.

I am not with HAL. With ALK or ASA. Retiring in June.

shroomwell

You also had to have three arms so that you could somehow press "hold" simultaneously on all three units when it was time to do a position and/or 10-minute check for the plotting chart.

Rama

Remember the Carousel INS well. 9 waypoints loaded, went direct to the last one than loaded 8 more. Rough flying Europe where you may have 60+ waypoints on a 5 hour flight.
A lot of drift was allowed, 3T +3. 5 hour oceanic crossing meant you could be 18 miles off and it was within limits.

TiredSoul

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