AP Use

Okay, who chooses to align themselves with setting the altitude preselect below ground level? Go on, identify yourself. It seems I'm too inexperienced to know any better, so who out ther supports this stupid practice?


Doug?
 
Clark1961 said:
Interesting. Haven't seen (or heard of) a runaway trim on the IIIc. Analogue systems can be difficult, that's for sure.
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Both of the Navajos I fly have this tendency on their IIICs. It gets annoying.
 
Captain said:
Okay, who chooses to align themselves with setting the altitude preselect below ground level? Go on, identify yourself. It seems I'm too inexperienced to know any better, so who out ther supports this stupid practice?
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It's not something we do.
 
Clark1961 said:
Do the guys in Mineral Wells have any comment on this?
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The one owner sent his out (I think to AP Central), gave them a bunch of money, and upon return it did the same thing. So he simply gave up. He then told the other owner this story, and advised him not to waste his money.

Neither Navajo is my plane, so my influence is minimal. I'd just shotgun it and get a 55X.
 
Captain said:
Okay, who chooses to align themselves with setting the altitude preselect below ground level? Go on, identify yourself. It seems I'm too inexperienced to know any better, so who out ther supports this stupid practice?


Doug?
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Maybe you only do that when flying around the mountain??? :dunno:
 
When is it OK or reasonable to set the preselect to an altitude below the surface??
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I really don't know. I'm not aware of any circumstances when it's okay to preselect an altitude below the surface. I've never done it. I don't think anyone in this thread has suggested they do it. I don't think the original poster has suggested he flies with people who do it. Who does this?

Perhaps I misunderstood. I believe some other posters indicated that they set field elevation; why, I don't know. Setting the alerter below field elevation isn't something I believe I'd do, and I'm not familiar with programs which advocate such. I'm also not familiar with all programs or methods, so won't decry something until it's been explained or demonstrated. If others are teaching such a program, then I'd be interested in the rationale, if I were learning to operate that equipment.

In post #39, Wayne indicated that he instructed in the GV sim and spoke of using field elevation procedures. AWACSEng also indicated using field elevation. It was this practice to which I referred.

(You're up late aren't you? It's what? about 0136 local in Afghanistan)
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It's about ten thirty in the morning here in sunny Afghanistan, and yes, I was up late.

The IIICs have a tendency to do runaway trim at random.
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I've had that happen in a Seneca II with the Century III.

I've had it happen in the C-130 and Learjet too, although obviously not with a Century autopilot. It can happen.
 
DouglasBader said:
I really don't know. I'm not aware of any circumstances when it's okay to preselect an altitude below the surface. I've never done it. I don't think anyone in this thread has suggested they do it. I don't think the original poster has suggested he flies with people who do it. Who does this?

Perhaps I misunderstood. I believe some other posters indicated that they set field elevation; why, I don't know. Setting the alerter below field elevation isn't something I believe I'd do, and I'm not familiar with programs which advocate such. I'm also not familiar with all programs or methods, so won't decry something until it's been explained or demonstrated. If others are teaching such a program, then I'd be interested in the rationale, if I were learning to operate that equipment.

In post #39, Wayne indicated that he instructed in the GV sim and spoke of using field elevation procedures. AWACSEng also indicated using field elevation. It was this practice to which I referred.


It's about ten thirty in the morning here in sunny Afghanistan, and yes, I was up late.



I've had that happen in a Seneca II with the Century III.

I've had it happen in the C-130 and Learjet too, although obviously not with a Century autopilot. It can happen.
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Yes, post #6 I brought it up. You then suggested my experience was lacking.
 
DouglasBader said:
Perhaps I misunderstood. I believe some other posters indicated that they set field elevation; why, I don't know. Setting the alerter below field elevation isn't something I believe I'd do, and I'm not familiar with programs which advocate such. I'm also not familiar with all programs or methods, so won't decry something until it's been explained or demonstrated. If others are teaching such a program, then I'd be interested in the rationale, if I were learning to operate that equipment.

In post #39, Wayne indicated that he instructed in the GV sim and spoke of using field elevation procedures. AWACSEng also indicated using field elevation. It was this practice to which I referred.
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I think I see what Wayne is saying. Using VNAV the autopilot would level off at a DA(H) instead of continuing down. We use VGP in that situation (arm APCH mode instead of using VNAV) so the autopilot will continue down, just as on an ILS glide slope.
 
You're a piece of work, arn't you?

So now you agree it's poor form to set the preselect below ground?
 
DouglasBader said:
I've had that happen in a Seneca II with the Century III.

I've had it happen in the C-130 and Learjet too, although obviously not with a Century autopilot. It can happen.
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Certainly it can happen on a number of different autopilots. They can all break. Of my limited turbine experience, the KFC200 or 300 (I can't remember which one it was - installed in a Cheyenne II) is the nicest one I've flown. Rock solid autopilot that is locked onto the course it's supposed to track. Of course, I'm sure people have had those APs break as well.

About a year ago, I was doing a transition for a jet pilot into a Bonanza with a KFC150. Their inclination was to hit the AP shortly off the ground and just fly it that way, being the SOP in the jets they fly. The KFC150 is a good AP, but this one had a few quirks in it, and isn't up to the sophistication of the AP he's used to in the plane.

Moral of the story is that I've noticed that APs in piston aircraft are typically not as good as turbine APs in the older planes we fly. They weren't as good to start out with, and as they've deteriorated they've gotten progressively worse. Turbine APs can still have problems and not work, but they were typically held to a higher standard to begin with. What's nice about modern piston APs is that they have come a long way, and are probably up to the level that turbine APs were a few decades ago.
 
FWIW, the King 300 didn't sell well and very few were installed. Even fewer shops are capable of repairing and servicing them. If anybody knows of one, please advise. We're struggling with one in an F-90 now.

Ted DuPuis said:
Certainly it can happen on a number of different autopilots. They can all break. Of my limited turbine experience, the KFC200 or 300 (I can't remember which one it was - installed in a Cheyenne II) is the nicest one I've flown. Rock solid autopilot that is locked onto the course it's supposed to track. Of course, I'm sure people have had those APs break as well.

About a year ago, I was doing a transition for a jet pilot into a Bonanza with a KFC150. Their inclination was to hit the AP shortly off the ground and just fly it that way, being the SOP in the jets they fly. The KFC150 is a good AP, but this one had a few quirks in it, and isn't up to the sophistication of the AP he's used to in the plane.

Moral of the story is that I've noticed that APs in piston aircraft are typically not as good as turbine APs in the older planes we fly. They weren't as good to start out with, and as they've deteriorated they've gotten progressively worse. Turbine APs can still have problems and not work, but they were typically held to a higher standard to begin with. What's nice about modern piston APs is that they have come a long way, and are probably up to the level that turbine APs were a few decades ago.
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wabower said:
FWIW, the King 300 didn't sell well and very few were installed. Even fewer shops are capable of repairing and servicing them. If anybody knows of one, please advise. We're struggling with one in an F-90 now.
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As I said, I can't remember if it was a KFC200 or 300. You'd probably know that better. All I know is that it worked beautifully in the plane last I flew it. Since it's now in central Africa, I doubt I'll be able to keep up on its maintenance from here forward.

Of course, once it stops working beautifully...
 
So now you agree it's poor form to set the preselect below ground?
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I've never selected below ground level, and never suggested it was good form.

As for a piece of work, you're the one calling people idiots and ranting about stupidity here. As I said, I was probably right.
 
Everskyward said:
I think I see what Wayne is saying. Using VNAV the autopilot would level off at a DA(H) instead of continuing down. We use VGP in that situation (arm APCH mode instead of using VNAV) so the autopilot will continue down, just as on an ILS glide slope.
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On the B757/B767 the procedure to use when doing an non precision approach or RNAV is crossing the initial approach fix to dial down the altitude to field elevation ( round up to next hundred, of field is 560 then put 600 in ALT on the MCP)

When the Altitude Range Mark on the ND aligns with the runway threshold and the aircraft has captured the glide path in VNAV then put the missed approach alt in.

This creates a glide path on the PFD as well as the ND and allows the jet to be flown on a constant descent angle.
 
DouglasBader said:
I've never selected below ground level, and never suggested it was good form.

As for a piece of work, you're the one calling people idiots and ranting about stupidity here. As I said, I was probably right.
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Really? If I've called anyone an 'idiot' or said what they do is 'stupid' I'd certainly like to apologize with all my heart. Please provide the quote.
 
According to the record (the one you claim doesn't exist) this happened in July 2006 near Filmore, Utah and the aircraft lost power and landed in a field. Seems the damage was a "knocked off tail wheel" and a blown aft seal on the engine.
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It didn't happen at Fillmore, and it wasn't in a field. The tailwheel wasn't knocked off. The rear turbine bearing seal failed.

The pilot didn't note the oil loss when he checked the resorvoir. He noted it in the bottom of a burning basin when he applied power and got temperature and no torque.

The oil resorvoir wasn't checked until several days later. The thick black smoke coming out of the intake after the aircraft came to a rest was a good indication that something was wrong, though.

I was on scene for two weeks on the mountainside following that event. I didn't see any FAA inspector present. Perhaps he "investigated" by flipping through the OAS report and summarizing what he thought he read. The inspector with whom I spoke stated quite clearly that he wasn't interested, and that his office didn't have the budget to come look, or to investigate the matter. He also noted that because it would be handled by a different agency, the matter was covered.

I've been involved in more than one such incident over the years in varying capacities; the FAA neither investigates nor involves itself in all of them. If you choose to believe otherwise, or choose to believe that the ASIAS file is an "investigation" or even an accurate representation, then more power to you. As I said before, whatever helps you sleep better at night. It won't change what occurred before, or after.
 
Can we please keep our conversations from devolving into shouting matches?
 
Captain said:
Also, because they want the plane to descend and not capture an altitude they spin the altitude preselect all the way down to subterranean.

Just seems bad form to set an altitude in the preselect that's lethal to fly. Sort of like building a fix inside a mountain.
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VNAV approaches have us set the altitude to 0. It seems a little low to me too. I prefer to set field elevation.
 
RotorAndWing said:
On the B757/B767 the procedure to use when doing an non precision approach or RNAV is crossing the initial approach fix to dial down the altitude to field elevation ( round up to next hundred, of field is 560 then put 600 in ALT on the MCP)

When the Altitude Range Mark on the ND aligns with the runway threshold and the aircraft has captured the glide path in VNAV then put the missed approach alt in.

This creates a glide path on the PFD as well as the ND and allows the jet to be flown on a constant descent angle.
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So in that way I guess you are creating your own glide slope? It won't follow the "regular" LNAV/VNAV glide path?
 
Everskyward said:
So in that way I guess you are creating your own glide slope? It won't follow the "regular" LNAV/VNAV glide path?
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The pilot has to create the glide path.

Remember the B757/B767 is 30 year old technology.

This may be where the confusion is concerning rolling down altitude to runway elevation.

Conversely, the A-320 will create it's own glide path on an RNAV approach.

Just depends upon the technology of the aircraft and systems.
 
RotorAndWing said:
The pilot has to create the glide path.

Remember the B757/B767 is 30 year old technology.

This may be where the confusion is concerning rolling down altitude to runway elevation.

Conversely, the A-320 will create it's own glide path on an RNAV approach.

Just depends upon the technology of the aircraft and systems.
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Makes sense.

The "older" aircraft I flew weren't even capable of this. We just used the "dive and drive" method.
 
Boeing actually has had ads shown on prime time TV showing the difference between VNAV and 'dive and drive'.

What they expect the general public to gather from that I don't know but the fact remains the commercials exist. Remember the rock diver?
 
My apology. Just trying to correct a few "facts".
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You didn't. Your "facts" are wrong. Your approach is also wrong, and as you well know, inappropriate.

The pilot has to create the glide path.

Remember the B757/B767 is 30 year old technology.

This may be where the confusion is concerning rolling down altitude to runway elevation.
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I fly a classic 747, which is even older technology, and we don't run the alerter down to the field elevation for an RNAV or RNAV/VNAV approach.

We do follow the altitudes down for each step fix, even though we're doing it as a constant descent, with the alerter. We fly it either with the manual pitch trim wheel (my preference) or off the vertical speed wheel, and follow a vertical path deviation indicator ("chinese glide slope).

We train for both constant descent approaches and for dive and drive, and the preference is to make all procedures that aren't ILS, that can be called up in a database, into constant descent. Accordingly, we fly the VOR or NDB (which we do train for and demonstrate) the same as a basic RNAV.

Our alerter and radar altimeters are set to MDA plus 50'. Any other time, precision approach or a step-down "dive and drive," the alerter is set to the missed approach altitude after we're done stepping down, or in the case of an ILS once glideslope intercept/capture has occurred.
 
DouglasBader said:
I fly a classic 747, which is even older technology, and we don't run the alerter down to the field elevation for an RNAV or RNAV/VNAV approach.

We do follow the altitudes down for each step fix, even though we're doing it as a constant descent, with the alerter. We fly it either with the manual pitch trim wheel (my preference) or off the vertical speed wheel, and follow a vertical path deviation indicator ("chinese glide slope).

We train for both constant descent approaches and for dive and drive, and the preference is to make all procedures that aren't ILS, that can be called up in a database, into constant descent. Accordingly, we fly the VOR or NDB (which we do train for and demonstrate) the same as a basic RNAV.

Our alerter and radar altimeters are set to MDA plus 50'. Any other time, precision approach or a step-down "dive and drive," the alerter is set to the missed approach altitude after we're done stepping down, or in the case of an ILS once glideslope intercept/capture has occurred.
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The 747's you fly have been updated in their avionics and FMS, I'm familiar with what you are flying with, hence why your procedure is different.

The B757/767 are using the same autoflight/FMS systems they were designed with, the exception of the flat panel displays being driven by them versus the original EFIS panel. Different architecture than that of the newer systems found in the newer 777,737, etc. The newer 767's coming out of Renton as I understand will have the new avionics architecture.
 
The avionics we've got aren't very new, but our authorization to do the constant descent procedures only started about a year and a half ago. Up until then, we still had to do "dive and drive" procedures. In fact, every recurrent up until then involved raw data hand-flown NDB procedures, among other things.

We've still got Litton 92's in the third position on the pedestle. The other two INS units are fronted by Canadian Marconi CMS900 FMS units, and the information delivered via a Sperry flight director to the EADI, and basic map information on an EHSI. Even with the upgrades, most light airplanes flying with Garmins have much more advanced capabilities than we do. We still have to use manual switching to fly a back course, and even then it only alters the flight director orientation; it's still got to be conducted manually. Low-tech, but it works.
 
DouglasBader said:
The avionics we've got aren't very new, but our authorization to do the constant descent procedures only started about a year and a half ago. Up until then, we still had to do "dive and drive" procedures. In fact, every recurrent up until then involved raw data hand-flown NDB procedures, among other things.
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Question for you from someone NOT familiar with commercial airline ops - on your constant descent procedures, do you target a minimum-thrust descent? Or some particular descent rate that is low-thrust? Dependent on load/conditions?

I know I've been on many SWA flights where they cut power (sounds like all the way back to flight idle) from cruise altitude and it doesn't come back up until vectoring for final, but that is highly dependent on time of day and airport of arrival (traffic levels, I suppose).
 
airguy said:
Question for you from someone NOT familiar with commercial airline ops - on your constant descent procedures, do you target a minimum-thrust descent? Or some particular descent rate that is low-thrust? Dependent on load/conditions?

I know I've been on many SWA flights where they cut power (sounds like all the way back to flight idle) from cruise altitude and it doesn't come back up until vectoring for final.
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Ideally the descent is done with idle thrust for economy.

The FMS is set up with a "Cost Index" number supplied on the flight release. This is an optimization for climb, cruise and descent.

As with most things, traffic and weather, ATC delays will affect descent profiles.
 
There's also some places where you just have to go down quick...

I hear 737's pop out the boards all the time on this arrival trying to slow up... usually near PAYDD or between there and HUUGE. (Which is an awesome name by the way.)

Sounds like someone switched on a giant vacuum cleaner southwest of town. I watch from the back porch.

For some reason the 73's seem to do it more often than other types.

The plate says to expect 17,000/250 but the usual given by the TRACON is 11,000/250. If DEN is busy it usually then also comes with a speed restriction.

Pop and drop usually happens right after that radio call if I'm listening with the handheld.

4b94241c-b996-c823.jpg
 
denverpilot said:
The plate says to expect 17,000/250 but the usual given by the TRACON is 11,000/250. If DEN is busy it usually then also comes with a speed restriction.
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We almost always get LARKS at 17,000'/250 knots and we have an even shorter distance to descend into Centennial. You need to be fairly aggressive on the descent or you will end up high.
 
Everskyward said:
We almost always get LARKS at 17,000'/250 knots and we have an even shorter distance to descend into Centennial. You need to be fairly aggressive on the descent or you will end up high.
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Heh. Cool. I never thought about you guys dropping into APA from LARKS. Wheee!
 
airguy said:
Question for you from someone NOT familiar with commercial airline ops - on your constant descent procedures, do you target a minimum-thrust descent? Or some particular descent rate that is low-thrust? Dependent on load/conditions?

I know I've been on many SWA flights where they cut power (sounds like all the way back to flight idle) from cruise altitude and it doesn't come back up until vectoring for final, but that is highly dependent on time of day and airport of arrival (traffic levels, I suppose).
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SFO is (was?) playing with a very interesting automated ATC architecture. ATC uploads a flight profile to some participating aircraft coming across the Pacific that keeps the plane at max altitude to the last second then gives them a power off descent profile to the runway with no level offs on the way. Reportedly it saves a hell of a lot of fuel.
 
Henning said:
SFO is (was?) playing with a very interesting automated ATC architecture. ATC uploads a flight profile to some participating aircraft coming across the Pacific that keeps the plane at max altitude to the last second then gives them a power off descent profile to the runway with no level offs on the way. Reportedly it saves a hell of a lot of fuel.
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I've seen that used a lot in the bizjet world, but usually at airports with no (or low) commercial activity so traffic was not nearly as big a factor.
 
I believe there's a similar project like that in MIA or JAX or TPA with SWA airliners, they have a STAR that is based on an idle descent profile.
 
Everskyward said:
I think I see what Wayne is saying. Using VNAV the autopilot would level off at a DA(H) instead of continuing down. We use VGP in that situation (arm APCH mode instead of using VNAV) so the autopilot will continue down, just as on an ILS glide slope.
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Yep, after discussing this very topic today, my original post was confirmed/clarified. For RNAV/VNAV approaches, once inside the final stepdown fix, field elevation (not bellow field elevation) is set. For other precision or non- precision approaches (ILS/LOC/ADF/TCN), DH/MDA is set. I don't know if this clears anything up, or adds fuel to the flames. Just the way things are done in our corner of the world.
 
Henning said:
SFO is (was?) playing with a very interesting automated ATC architecture. ATC uploads a flight profile to some participating aircraft coming across the Pacific that keeps the plane at max altitude to the last second then gives them a power off descent profile to the runway with no level offs on the way. Reportedly it saves a hell of a lot of fuel.
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While we don't do a descent at flight idle, that's what I aim for in the Commander to the greatest extent practical. It does save quite a bit - the plane burns as much at holding speed at 4,000 ft as it does at FL270.
 
Question for you from someone NOT familiar with commercial airline ops - on your constant descent procedures, do you target a minimum-thrust descent? Or some particular descent rate that is low-thrust? Dependent on load/conditions?
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For us, constant-descent is something we do during an approach, rather than an arrival. It's rare to arrive somewhere that one can make a constant descent from altitude. Invariably there will be level-offs along the way for many different reasons.

During an approach, of course, we don't go for minimum thrust, but use what thrust is needed based on the airspeed and aircraft configuration. For us, once configured on the glideslope, total fuel flow at the approach thrust settings is in the ballpark of about 24,000 lbs/hour. It's a handy figure, because for four engines that's about six thousand pounds an hour each. If it's a three-engine approach, it's still 24,000 lbs and hour, but this time with increased power on three engines, at about 8,000 lbs/hour on each engine. Those are rough, ballpark numbers, but you get the point.

The speed varies considerably on the approach; at our max gross landing weight of 630,000 lbs, we'll have a much higher approach speed than at an empty weight of around 370,000 lbs. At those weights, our final approach speed is quite low, around 120 kts. At gross, it's higher, around 160 knots. The power required varies quite a bit between the two extremes.
 
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