Is it a bird? A plane? VNAV? ...No,

[Rotten Apple #1]

It's ALT HOLD. (At least I think so)

Seeing as it's a slow controversy week on AvCanada (well, except for the Sunwing vs Group TransAt superbattle underway elsewhere on this forum), and it's Friday, here's the skinny on the latest "omigod I can't believe it just did that!" from Jonny.

So we are headed into Vegas a while back and we get that routine "Descend and Maintain FLxxx or die" instruction from LA center. My colleague, of a like mind as I, decides to descend in V/S mode at 1500 ft/min.

When we level off at FLxxx, my colleague pushes the VNAV button on the MCP and calls "VNAV". I then look at the FMA, when what to my wondering eyes should appear, but...well ALT HOLD.

What to respond? Think I with much wonder...

If Ian Fraser were here, would the cockpit resonate with thunder?

Because we descended in VS before the TOD the FMS did not transition to DESCENT phase so it still thought it was in CRUISE phase when my partner pushed the VNAV button. The window blanked and the VNAV light illuminated but the FMA showed ALT HOLD.

When the altitude selector was later rolled to a lower altitude the "VNAV Disconnect" message showed in the FMS.

Just a Friday afternoon conundrum provided free of charge by your friendly neighbourhood Jonny Dangerous.

Would you respond VNAV or ALT HOLD? EDIT: Or "Cheeeeeeck", as Balfour correctly points out below?

[Rotten Apple #1]

And please have several drinks before responding, if at all possible.

[moe]

vnav hold.... haha

[wrc]

I'll bite. Why did he descend in V/S?

Or as a Boeing Audit pilot told another WS Crew doing another FMA thing, "don't you think we thought of that?"

[balfour]

Well Johnny, after many years of having "read the fuckin' FMA" drilled into our heads, I would still say "cheeeeeck".

As you and I both know, it's not a mandatory call unless he's hand flying. That also opens up another big ole can o worms.

Happy drinking!!!

[wrc]

Oh BTW, don't get me wrong, nothing says you can't do that. It's just a bit of a make work project. Kind of like the guys who won't stop forwarding logbook pages after being told to stop or as DR said, "all they've got to do is....nothing, and they still won't stop".

Granted, part of my philosophy is based on sheer laziness but also the idea (shared by Boeing) that every unwarranted input is a potential point of error (as your incident illustrates) and distracts from flight monitoring and S/A.

[Rotten Apple #1]

WRC, I believe the descent instruction was something along the lines of "and give me 1500 ft or greater".

In a place like Vegas, where step descents are the norm, using V/S and letting it go into ALT HOLD followed by V/S again etc is probably less labour intensive than that whole "set new cruise..." go-ahead. No?

And BTW, after the Helios incident I would say the answer to mr smarty pants Boeing guy's question "don't you think we thought of that?" Would be: "I'm not sure".

[Ryan Coke2]

Well you provided the pre-emptive response to 'why did you feel the need to descend at 1500 fpm--just because you were in the states??'. But that is worthy of a couple of pages of debate on it's own.

And 'not mandatory unless they are hand flying'....well they need to call the mode change, and if the mode called doesn't match the mode annunciated then the PNF needs to verbalize the problem, so I have no idea what doesn't apply unless your hand flying in this case.

But more than anything that is really cool, in a bizarre I can't believe you were able to confuse the airplane like that way. Never seen that before.

[Rotten Apple #1]

Okay, before Ian F. calls me Monday morning with a 'cease and desist' order, I only observed the above mentioned phenomena I didn't create it.

WRC, I can't remember, has SouthWest authorized their pilots to use VNAV yet?

It was interesting though to see the FMA read:

FMC SPD............LNAV..............ALT HOLD

I can't remember if the bus allowed such a combination. Anyone? Bueller?

[wrc]

I'm glad you did the pre-emptive "asked for 1500". Pet peeve when I hear, "they need 1500 in the states", obviously in your case he asked for it, but in my ATS past I can't recall anything about 1500+. Another case of, why would Boeing put in a default that 80% of thier customers can't use. But as Ryan points out, that's a whole other debate. Although interestingly, a min of 1000 is a good idea for radar trend recognition.

As for descent, alt int followed by V/S should solve any issues. Also, unless you're way back and going to get a nasty messege, I don't see the need to be resetting the crz on step descents, but then, that's the input/laziness thing kicking in again...

As for the Helios thing, ya can't protect everyone from themselves if they're bent on self destruction although it further backs up my claim that the vast majority of misery is self induced

[Rotten Apple #1]

Well I'm not sure the Helios crew was bent on anything; did you read that in the official report?

Seems a bad human factors design; Boeing's lawyers must agree as there's a new light in the cockpit that will be activated soon.

Not slagging Boeing here. Confusion arising from unforeseen situations happens to all manufacturers (check out the early A320 accident where the crew confused FPA w/VS). Helios was no different. Bad set up. One horn, two meanings.

[swordfish]

from http://www.b737.org.uk :

14 Aug 2005; 5B-DBY, 737-300, 29099/2982, Del 15/1/98, Helios Airways; Grammatiko, Near Athens, Greece:

The aircraft departed Larnaca at 06:07 GMT for Athens. As the aircraft climbed through 16 000 ft, the Captain contacted the company Operations Centre and reported a Take-off Configuration Warning and an Equipment Cooling system problem. At 06:26 the crew said that they had solved the problem and requested a climb to 34,000ft. Radio contact was lost with the aircraft at approximately 06:37, 30 minutes after its departure, although it did squawk 7700. Greek F16s intercepted the aircraft at 07:20 and reported that the Captain was not visible and that the F/O appeared to be slumped over the controls. Two mayday calls were recorded on the CVR at 08:54, some reports say that a cabin crew member with a PPL licence was in the flight deck at impact. The aircraft crashed into mountains at 09:03 GMT after running out of fuel approx 19NM North of LGAV near the village of Grammatiko, the passenger oxygen masks had deployed. All 115 pax and 6 crew died.

Depressurisation is the probable cause but why the crew were not able to use their oxygen and descend the aircraft to safety is still a mystery. The FDR was recovered immediately but the CVR was in poor condition. Autopsies found that those crew and passengers examined were alive on impact possibly indicating that they suffered from a lack of oxygen and were unconscious. The same aircraft has had a history of pressurisation related problems and suffered a loss of cabin pressure on 20 Dec 2004 in flight from Warsaw to Larnaca.

A summary report issued 10 Oct 2006 states "The direct causes were:

• 1. Non-recognition that the cabin pressurization mode selector was in the MAN (manual) position during the performance of the Preflight procedure, the Before Start checklist and the After Takeoff checklist.
  2) Non-identification of the warnings and the reasons for the activation of the warnings (Cabin Altitude Warning Horn, Passenger Oxygen Masks Deployment indication, Master Caution).
  3) Incapacitation of the flight crew due to hypoxia, resulting in the continuation of the flight via the flight management computer and the autopilot, depletion of the fuel and engine flameout, and the impact of the aircraft with the ground." It also acknowledges that a contributory cause was the "omission of returning the cabin pressurization mode selector to the AUTO position after non-scheduled maintenance on the aircraft".

[jjj]

Nothing wrong with using V/S in a descent. However it can sometimes get away on a person if the descent is made before changeover. As one descends the autopilot maintains selected mach and can sometimes go beyond the planned transition speed. It gets everyone once as they changeover and realize that they are now doing 310 knots vs. a planned 260 or so.

As far as what descent is required you actually have to be a mind reader. Regardless of the regs - one controller wants 1000 fpm and the next wants 1500 or 2000 fpm.
On receipt of clearance just query the controller and all will be easy.

As far as resetting cruise altitude as a controller steps you down early - it is not generally required or necessary except in the instance where you are cleared to descend to a certain FL with a restriction and then further cleared to a lower level at your discretion. Resetting the intermediate cruise altitude allows you then to put your lowest cleared altitude in the MCP which is most desirable. Or perhaps if you descend to FL360 from 400 due to bumps and use altitude intervention, depending on how far from destination and amount of reserve fuel - you can get a "using reserve fuel message." Resetting cruise altitude in this case is absolutely appropriate.

The guys that say "never use V/S at altitude" or "you must always reset your cruise altitude" or "always select a hard altitude on the legs page by deleting the A from a 3000A at a DTW" or we should "never overwrite 240 below 10000" and so on - should really spend more time on their days off studying.

However, despite these people's lack of understanding - ultra conservative methods will rarely get them into trouble.

Never say never.

[jjj]

Regarding the original question...

When the pilot selected VNAV at the lower altitude perhaps he was expecting VNAV ALT to show up on the FMA.

I suspect that that ALT HOLD activated as a reversion mode because the aircraft's FMC was not in descent mode.

If the pilot descended in V/S then also selected altitude intervention the FMC would have entered descent mode. Upon selecting VNAV he would have gotten his desired result.

As far as I can tell - VNAV ALT will only activate when the FMC is in climb and descent and if I understood the problem I believe the FMC was still in cruise.

Will research this some more.

[wrc]

Oh BTW, don't get me wrong, nothing says you can't do that. It's just a bit of a make work project.

You can do descents a hundred different ways, read all the tech. books you want, forward and backward, yet still deviate from the 'design philosphy'. It's one area we're a bit weak in our training, maybe for good reason as the flood of data in the initials requires it to be tuned to 'hard tasks'. KISS works very well on this A/C or as someone we all know amoungst the learned here said, "the guys who are 'experts' on that stuff are the ones we have to watch".

[Rotten Apple #1]

WRC,

thanks for this info:

Kind of like the guys who won't stop forwarding logbook pages after being told to stop or as DR said, "all they've got to do is....nothing, and they still won't stop".

I had an F/O tell me this some few pairings ago, and I responded that I thought the memo had initially said only on terminating flights for the day were we not to forward the log page. Consider me now up to date! I certainly wouldn't want to be creating headaches for anyone now would I?

Another software anomaly (if you will) on the NG's FMC illustrates a point that we front line guys must always been vigilant for computer idiosynchrocies (sp?):

This scenario occurs, from what I have seen, at only two destinations, CYOW and CYUL. If you enter (and execute) the CAPITAL arrival for CYOW into the box for the RNP (or BC) RWY 25, it will automatically generate a constraint at LANRK of "AT OR BELOW 16000 feet", as per the paper approach plate. If you were subsequently to get a runway change to the ILS RWY 07 the following would occur:

Upon entering and executing the ILS 07 (still with the CAPITAL arrival), you would verify the waypoints and expect the FMC to autogenerate the 'new' constraint at LANRK of "AT or BELOW 10000 feet", as per the paper plate. But guess what?

It doesn't.

It actually keeps the 16000 feet restriction. You have to overwrite the constraint and enter "100B" yourself. Funny wha?

This happens as I wrote earlier at CYOW and CYUL for a couple of arrivals each, where there are different altitude constraints at a waypoint depending on the runway. So far as I can tell (a BIG caution there...), it doesn't happen elswehere. I.E in YVR there's an arrival where there's an altitude constraint for one runway on the arrival and none on the other. When you do the runway change there, the FMC automatically erases the original constraint.

So keep those verifications going.

It's one reason why I never do an approach briefing now (when I'm PF) and say: "And you've verified the waypoints and altitudes". I always, always, always, refer to the LEGS page during my brief and compare the paper plate to the box. "It's one area we're a bit weak in our training". (IMHO).

Otherwise I might have gotten caught on a late change to plan during a runway change in YUL and done a hurried verification of the FMC and missed the FMC's 'forgetfulness' and responded 'waypoints and altitudes verified' when they really weren't and then heard the wrong altitude at that waypoint during the PNF's approach brief and realized my mistake and then had to write up an AQD. I might have had to do that...

Anyway. Trust no one. Even if he's made of silicone '1's or '0's or wears a hat that says he's from Boeing and says "Don't you think we thought of that?"

Is what I'd say.

And I'm not even an 'expert'.






EDIT:

WRC, I just re-read a post of yours and would like to categorically state (what the hell does that mean anyway, "categorically") that I buy into that philosophy you mention about unwarranted entries creating error opportunities. I have worked at eliminating those of my behaviours antithetical to that notion. The process continues.

Now about that logbook thing. Airline pilots are creatures of routine, probably more so as they age. It can take a while to unlearn repititious behaviours. Unlike SOPs which we have reference to in manuals....memos get lost amongst uniform sizing event notices or pizza party FYIs. It might seem easy in cubicle land to regale the water cooler crowd about how we're just asking people to do nothing and get the obligatory laugh, but when you're working from one end of the country to the other and just got barely enough time to complete a landing calculation flowchart contraption, sometimes minutia about filling out (or not) logbook gets lost. Whew. All in one breath

PS Bobble-Head Jonny Dangerous dolls are now for sale in dashboard size for easy mounting on the glareshield. Going fast...

JD

[Clint23]

WRC,

thanks for this info:


Quote:
Kind of like the guys who won't stop forwarding logbook pages after being told to stop or as DR said, "all they've got to do is....nothing, and they still won't stop".



I had an F/O tell me this some few pairings ago, and I responded that I thought the memo had initially said only on terminating flights for the day were we not to forward the log page. Consider me now up to date! I certainly wouldn't want to be creating headaches for anyone now would I?



Hey JD, I agree with you!

I thought it was only on terminating flights as well. What difference does it make if the incomming or outgoing Capt transferrs the totals to the next page? Not until the AME totals the logbook at the end of the day and signs off any corrections does it make a difference. Me thinks we need to ressurect that memo and take another look!

Cheers

[wrc]

In the world of procedural violations, I think the log book thing is pretty low on the scale It's only funny because it actually involved LESS work and he still couldn't get us to do it right.....

[MS737]

Hey Jonny D, did you select the arrival again when you changed runways. From what I can remember in training you have to do this, and clean up the legs pages when you verify the waypoint and altitudes as there will be a discon between the old arrival-approach and the new arrival-approach, hence verifying everything. This should fix that, although I am kinda guessing here. Been a little while since I read the book. Here's another one. Going into YYJ we were on the new APASS 1 to runway 09. When reselecting the runway with the IF transition and arrival again, the FMC built in a discon between the YYJ VOR which is what we were flying to at the time, and the new arrival-approach. The ND screen showed a normal magenta line from where we were to the DTW because the new arrival overlaid what we were flying at the time. What it didn't show was the discon after YYJ. Kinda surprised us as the plane didn't make the turn. As you said, verifying waypoints and altitudes is critical, especially when runway changes occur. Cheers

[commuter]

The guys that say "never use V/S at altitude" or "you must always reset your cruise altitude" or "always select a hard altitude on the legs page by deleting the A from a 3000A at a DTW" or we should "never overwrite 240 below 10000" and so on - should really spend more time on their days off studying.

I agree 100% !

[Rotten Apple #1]

Sorry MS737, a little late in responding.

Actually I tried a number of things on later flights to see what would rectify it (including pulling out the SUPPLEMENTAL PROCEDURES section in the FOM to confirm what was required). Nothing made a difference. If you want to change the restriction, you must manually insert it, OR, delete the restriction first, and then select the ARRIVAL and APPROACH (and execute, of course).

[E-Flyer]

FLCH

[FICU]

Well I'm not sure the Helios crew was bent on anything; did you read that in the official report?

Seems a bad human factors design; Boeing's lawyers must agree as there's a new light in the cockpit that will be activated soon. happens to all manufacturers (check out the early A320 accident where the crew confused FPA w/VS

Not slagging Boeing here. Confusion arising from unforeseen situations ). Helios was no different. Bad set up. One horn, two meanings.

Not to derail the thread but the Helios accident was more pilot error than any other factor. How many times in the checklist is the air conditioning and pressurization panel manipulated and or looked at?

1. F/O initial flow with the Capt. watching.
2. Captain initial flow with the F/O watching.
3. Before start checklist to the line.
4. Below the line.
5. After start checklist.
6. After take-off checklist.
7. 10,000 foot checklist.

7 times the crew could have/should have saw the green "Manual" light and the mode selector not in "Auto".

The inadequate F/A training and procedures was the final factor that prevented a safe outcome.

Not Boeing's fault IMO but of course they had to do something to add another level of redundancy to make sure it never happens again.

[Ryan Coke2]

As in any accident there were certainly several layers of 'swiss cheese' that the accident chain made it through, but it is blatantly obvious that it is a poorly designed system from a human factors standpoint.

Having flown the 37 for several years now I can easily see how airplane design assisted in the errors made with Helios.

[Rotten Apple #1]

Not to derail the thread but the Helios accident was more pilot error than any other factor. How many times in the checklist is the air conditioning and pressurization panel manipulated and or looked at?

1. F/O initial flow with the Capt. watching.
2. Captain initial flow with the F/O watching.
3. Before start checklist to the line.
4. Below the line.
5. After start checklist.
6. After take-off checklist.
7. 10,000 foot checklist.

7 times the crew could have/should have saw the green "Manual" light and the mode selector not in "Auto".

The inadequate F/A training and procedures was the final factor that prevented a safe outcome.

Not Boeing's fault IMO but of course they had to do something to add another level of redundancy to make sure it never happens again.

Well there must be some reason (besides just 'pilot error' on a single occurence incident) that Boeing is now making deliveries with NGs having a better means ( 'UNIQUE FUNCTION DEVICE') of alerting the crew to a cabin pressurization problem, than a dual purpose horn. They don't do these things out of the goodness of their heart, now do they (anyone smell a lawyer)?

And what's up with having a 'GREEN' light to indicate the pressurization system in 'ALTN' mode (green is a 'normalish' color to my simple brain)? Just a thought...

Anyway, a great bird to fly. It pays my mortgage, and then some.

JD