The Great Ongoing Aviation Thread (general and other)

Miscellaneous and Personal Stuff I Must Share
561

A few questions for those of you who are or have been commercial pilots, contemplated based on my continued exploits in FSX:

[ul]
[li]What percentage of time do you spend, during a typical flight, using autopilot functions? Is it generally the entire time you’re at cruising altitude? More? Less? Not at all?[/li][li]Are you often executing heading and altitude changes by manipulating the autopilot settings, rather than handling the stick/yoke?[/li][li]To the extent you use autopilot functions, do you typically use all of them (speed, altitude and heading holds, as well as any others I’m not aware of), or only specific ones?[/li][li]Again, assuming you do typically use AP, at what point, specifically, during the flight would you tend to switch back over to manually controlling the aircraft? I understand that one can have AP land the plane using ILS or similar, but I have also understood that isn’t something done regularly.[/ul][/li]I’m curious about autopilot use in general, so if there’s something I haven’t asked here that seems interesting to share, I’m all for it.

562

In my world the autopilot is turned on about 3 minutes after takeoff and is left on until about 10 minutes before landing. And I hand fly more than most of my peers.

On Airbus aircraft procedure is the autopilot is turned on about 10 *seconds *after you break ground and remains on until about 30 *seconds *before landing.

While the autopilot is on we operate the airplane in one of two modes: maneuver via the knobs & buttons on autopilot control panel, or slave the autopilot to the FMS and control the aircraft via typing on FMS. Typically the former (“George”) is used for the first & last 10-15 minutes of flight whereas the FMS (“HAL”) is used the rest of the time.

There is a concerted effort by the manufacturers and the FAA to do less and less of the George-style semi-hand-flying by the autopilot maneuvering panel in response to controller vectoring and more and more HAL flying by building FMS routes from liftoff to touchdown with are then executed by the FMS with only strategic interference by the pilots or the controllers. Needless to say, this approach all but mandates autopilot use from liftoff to near touchdown. And is the thin end of the wedge of fully, or at least mostly machine-flown airliners with one pilot on the ground for every couple dozen jets in the air. They also hope it’ll let them eliminate about 90% of the controller workforce and let AI’s watch & manage the traffic.

At present it’s not prohibited to completely hand-fly pretty much whenever and wherever you want. Some folks do more, some do as little as possible. There are certain low-weather high-precision events that must be machine flown.

Pretty much every autopilot mode gets used. Some much more often than others. For example, I’ve done exactly one localizer back course approach in the last 5 years. So that’s the last time I touched that button / mode. Almost all the other buttons / modes get used on almost every flight.
With all that background, here’s a typical flight with normal weather from end to end as I and most of my co-workers do it:

Hand-fly the takeoff and initial climb-out up to 5 or 6,000 feet above the field. So about 2-3 minutes worth. Once we’re done accelerating, cleaning up, and are pointed more or less where we’re going it quickly gets boring to hold heading/track & speed by hand. So basically if we’re doing something dynamic I’m hand-flying. If not, the autopilot is.

Once it’s pretty much “steady as she goes” for at least for the next few minutes I let George drive. We’re typically on radar vectors towards a departure track at that point and will be stepping upwards with new higher altitude clearances every couple minutes. That’s normally done with heading select and the basic climb/descent autopilot modes.

Usually around 15,000 feet we’ll get handed off to center & cleared direct to some point on our route. At that point we switch the autopilot to LNAV & VNAV and let the FMS = “HAL” control the autopilot. We then update speeds, desired lateral paths, and altitudes via the FMS keyboard.

HAL takes us to top-of-climb, all of cruise, and descent down to around 10,000 feet.

Somewhere around there we’ll hand off to approach control and begin again the vectoring, small altitude step-downs, and speed adjustments. At that point HAL is more trouble than he’s worth so we switch back to “George”: directly controlling the autopilot using heading select and either vertical speed or airspeed based descent modes, plus autothrottle speed control.

We’ll eventually get aimed towards an ILS beam and will configure the autopilot to capture & follow it down towards the runway. I usually switch to pure hand-flying at this point. Others will leave the AP on until about the final approach fix.

With the result that last 15 or 5 miles = 5 to 3 minutes to touchdown are hand flown. As is the touchdown and braking.

Some folks leave the autothrottles engaged almost to the flare and control speed that way. My habit is to very rarely use autothrottle with hand flying. It’s pretty much either all me, or all George.

Finally note that on modern airliners the flight director is integral with the autopilot. So whether we’re hand flying or not we’re still manipulating all the FMS or autopilot mode controls to keep the flight director synced with what we’re doing. In essence, the flight director is the brains that decides how to steer the aircraft to accomplish the maneuver smoothly and precisely and the autopilot is the muscles that substitute for mine when I let it fly.

This got kinda long, but it’s a big set of questions. I tried to give enough detail without getting lost in minutia. Ask again if you want more, less or different.

563

Thank you for that – I definitely wasn’t seeking any less than that. I’d always felt like I was being lazy using autopilot so extensively in FSX, so I’m glad to see that that’s actually the norm.

I have never heard of FMS before, so if you feel like expanding on that, I’m happy to read it. But I am also happy to go look it up!

564

This is a pretty good intro to FMS at the level you care about: Flight management system - Wikipedia

Bottom line, it’s a computer with a database of aircraft performance data and the equivalent of all the paper charts: SIDs, STARS, approach plates, and enroute hi & lo charts. It takes inputs from all the instruments including the IRS/GPS. It outputs various performance and predictions on its screen(s), and can output speed, throttle, and steering commands to the autopilot / flight director.

Before takeoff we program in the aircraft weight, fuel load, winds and temps aloft, and the planned route and altitudes of flight. As we fly along it uses the IRS/ GPS data to follow along.

Once ATC clears us to follow the planned route we tell the FMS “GO there” to someplace on the route, then connect the autopilot to follow FMS guidance. The FMS computes the course to get there & steers the autopilot to that course and makes adjustments for wind as we go along. When we get to “there”, it looks up the course to the next point on the flight plan & steers us there in turn.

The same kind of logic applies in the vertical dimension. It knows how high we can climb, what are the optimal speeds for this weight, wind, and temperature situation, any altitude wickets we need to fit through, etc. So it computes the optimal path. We follow that as best ATC will permit.

All along it’s doing all the grunt work of predicting ETA and fuel details for the rest of the flight considering the winds, temps, climbs, descents, etc.
When these systems were first installed on airliners pilots then were used to low tech autopilots that could barely manage straight-and-level and mostly hand-flew everything using VOR to VOR nav. So the joke was “I’ve forgotten how to fly but now I can type 60 WPM!”

This was also the origin of the joke about the crew of the future being a man and a dog. The man is there to start the computer & feed the dog. The dog is there to bite the man if he touches anything in flight.

565

I fly business jets, so my answer would be similar to LSLGuy’s. But I’ll add that the amount of “hands-on” time that is strictly necessary largely depends on the equipment. When I flew a turboprop at a regional airline our automation was pretty rudimentary, so we did a lot of hand flying.

If you’re just starting out as a commercial pilot and working in a Navajo or light twin, you might have nothing more than a wing leveler. At that stage of the game, I was happy if I had altitude hold. A coupled approach (meaning, the automation could fly a glideslope / localizer) was a luxury.

Nowadays though, your basic GA planes often come with better automation than some large-ish commercial aircraft. A Cirrus, for example, makes my former airline’s turboprop look like it ran on coal.

566

In the early 1990s I was teaching on the 727. We had guys coming to our airplane from the latest shiny RJs, the EMB-135 and CRJ. They could not comprehend how primitive the 727 avionics were. I told them to think back to their single Cessna days, but just make everything dual.

For comparison on the 727 we hand-flew from takeoff to top-of-climb and pretty much all of top-of-descent to touchdown.

Enroute we had altitude hold. The Captain had heading select slaved to his HSI heading bug. The FO had to make do with heading hold and a knob that controlled bank to turn.

And that was it for automation. Plus dual flight directors that were independent of, and usually didn’t agree with, the autopilot. 2 VOR, 2 ILS, 2 DME for nav.

I was a much better pilot then. As we all were.

567

Don’t feel guilty about using the autopilot in flightsim. For one it’s realistic, as LSLGuy says, to use it a lot in the real world, for another computer flight sims aren’t very good at giving a realistic hands-on flying experience so use it as much as you want.

One of the really nice things about working for a contract/charter company who’s fleet grows and shrinks regularly based on the work we have is that we have an astounding range of aircraft ;). Though they may all look the same from the outside some of our 146s are full analogue cockpits and a very rudimentary GPS (not worthy of the name “Hal”) and others have (partial) glass cockpits with dual FMS and auto-land. I think we still have a 146 that can’t navigate off the GPS, that is, you have to fly it in HDG mode everywhere.

As for use of the autopilot, it’s as LSLGuy said pretty much. An exception is that when flying our Avro RJs I engage the autopilot early, just after the gear comes up. I mainly do this because the flight director must be on (company requirement), and I can’t stand hand flying and not following the flight director (if you’re not going to follow it it should be turned off IMO.) In the acceleration phase of flight, just after take-off when the gear and flaps are coming up the flight director on the RJ commands some odd pitch changes that are not in sync with how I like to fly the aircraft. My choices are to hand fly and follow the flight director and not like what it is telling me, to hand fly and not follow the flight director and not like that I’m doing that, or engage the autopilot at 350’ and sit back and watch George follow the flight director. I normally choose the latter.

In our 146s the FD operates differently and I can fly how I want to and command the FD to sit where I want so I will typically hand fly the take-off at least till the flaps are up, but more commonly to somewhere between 5000-10000’, handing over to George when I get bored with it.

I will typically turn George off at about 1000’ on an ILS approach or 1500’ and on downwind if flying a visual circuit.

There is a deep unease in our industry that the use of automatics is degrading our manual flying skills. That may be true in general but I have not found it to be true personally and I feel no need to “practice” hand flying, I just do it if it is a nice day and I feel like it.

One thing to be cautious of when hand flying is that it gives the other pilot more to do. This may be trivial or it may not be. Normally the other pilot, “pilot monitoring” or PM, also known as the PNF or pilot not flying, is handling the radios and monitoring what the pilot flying is doing. If the PM is doing their job properly they should be mentally flying the aircraft so a part of their brain capacity is virtually flying the aircraft even though they’re not physically doing anything. In addition they handle the radios, make flap and gear selections, and read checklists, while saying all the right things at the right times. Sometimes the end result is low workload sometimes lots is happening at once and the workload is high. If the pilot flying wants to hand-fly then the PM has to manipulate the flight director, turn the HDG bug as required, reset the altitude window and speed selector etc. This is normally no problem but it is something for the PF to be aware of when they decide how much hand flying to do.

Flying relatively old aircraft as I do, we sometimes don’t get a choice about hand flying or not. I was recently flying an approach into Melbourne in less than ideal conditions, lots of turbulence with multiple aircraft flying missed approaches due to wind-shear. This is the sort of time you want to use the AP as much as possible but in the machine I was flying at the time, number 2 off the production line, the AP couldn’t handle it and kept disconnecting, so the last 5000’ of vectors from approach and the ILS was hand-flown because it had to be.

During my command line training and subsequent check I had several genuine AP failures that resulted in me hand-flying from take-off to landing.

The above incidents are why I don’t worry about practicing hand flying anymore, I know I can do it when I have to.

There’s a good lecture on youtube by an American Airlines guy about appropriate use of automation. https://www.youtube.com/watch?v=pN41LvuSz10. It may even have already been linked in this thread but it’s worth bringing up again. It is quite old now but still very relevant.

568

Yaw dampener ???

Saw a video of a airline size Russian jet or some place in Eastern Europe that had lost the yaw dampener and it was wallowing almost out of control as I saw it.

One of the big iron pilots said you almost never use your feet in a big jet.

So, my question is can a B-737 say, be hand flown without the yaw dampener working?

If you were unlucky enough to be in that situation, would the aircraft be more controllable if it is kept in a moderate turn?

Go to your crash place of choice by doing constant S turns so the lack of the yaw dampener does not put you in the trees?

Or are you just SOOL if you lose the yaw dampener?

I have heard that high altitude flight without the Y D is near impossible while in some airplanes it is not so bad down low…

Any help with this question???

569

My question about bleed air and leaky cabins:

2 identical aircraft, B Jets that seal up good, same engines, mods, load, equipment and the engines are in identical good condition.

One pressure vessel is in ‘tighty whitey’ condition and the other has air leaks that are not drag producing exterior defects.

Pick a low altitude, side by side, say 190, east bound and both are holding 10k cabin pressure. Leaky can not go another 1000 feet up and still hold the cabin pressure and Tighty is just using minimal bleed air to hold the cabin pressure.

Any difference in fuel flow between aircraft?

If they go 1000 feet higher and the Leaky aircraft is producing max bleed air possible and Tighty is laughing at him, any difference if Leaky is maxed out on bleed air delivery and Tighty has not reached 50% capacity yet? Yeah, Leaky leaks like a colander.

Any difference in fuel burn or engine strain?

So, if you never go high enough for what ever reason that you don’t max out the bleed air, does a leaky pressure vessel cost you anything. That is just the altitude you want to fly at so a tight pressure vessel at those same altitudes has no gain in efficiency?

Can you please lead me out of this maze? :confused:

570

In my experience, losing a yaw damper is mostly just a nuisance. High altitude can make it more worrisome - the small jet I fly is limited to 30,000’ with the YD inop. Depending on the aircraft you might not be able to use the autopilot without it, so there’s that too.

This reminds me of a great story which I believe appeared in Frank Borman’s autobiography. Borman was one of the Apollo astronauts and he had a reputation as a no-nonsense, ramrod stiff military guy. After NASA he became president of Eastern Airlines. So one day he was traveling on one of the company planes, and unknown to him, the yaw damper was inop. About halfway through the flight he asks to go up to the cockpit and says to the crew, “I don’t meant to tell you guys how to do your job… but my ass tells me this plane ain’t flying straight.”

With no change of expression, the captain calmly says, “Your ass is correct, sir.”

571

The finer points of the bleed air system is not my forte, but as I understand it the air conditioning packs deliver a constant flow and the pressurisation is controlled by changing how much the outflow valves open. That given, the demand on the engines is the same regardless of how leaky the cabin is and Leaky and Tighty will have the same fuel flow and strain etc. Leaky will have outflow valves that are nearly closed and Tighty will have outflow valves that are more open. In other words, the outflow valves adjust so that the leak rate of the fuselage as a whole is identical between both aircraft.

Yaw Damper

In the Quadrapuff the loss of the yaw damper is a non-event. You can feel it wallowing around a bit and it’s probably not the best for the rear passengers but it is no big deal. We don’t even have speed or altitude restrictions with it off and the aircraft can be flown with the yaw damper as a deferred defect.

572

Exactly as **LL **& RP have said so well. More details to follow, but you knew that already :D.
Pressurization, etc.:

The key thing about pressurized aircraft is they are not sealed in any meaningful sense. They’re more like a boat with holes in the bottom and big bilge pumps than like a sealed submarine.

An even better metaphor is this: They’re more like a bait tank. Big holes in the bottom to let the fish shit and used water out and big flow in the top so the fish always have something fresh to swim in.

All the air in the airplane is replaced every few minutes. Per cubic foot of volume, or per square foot of floor space there’s far more air turnover in an airplane than in a house or a store or an office. The only reason it sometimes feels a bit stuffy is the relative density of people. If you put the same density of people in a meeting room or restaurant it’ll get unbearable real quickly.

Beyond that your intuition is basically correct. If somehow less cabin inflow is demanded then less bleed air offtake will be demanded from the engines. Which improves their thermodynamic efficiency resulting in lower fuel flow and lower internal temps for the same thrust output.

Some aircraft take advantage of this. The 747 has 3 air conditioner units (“packs” in the argot). Any engine can supply bleed air, and typically 3 engines feed 3 packs on the ground and at low altitude on warm days. Once up in the cool, one pack and engine bleed is shut off. The remaining two put out plenty of airflow to keep the fish happy and less fuel is burned in the two non-bled engines. The difference is small percentagewise, but over many hours of flight times many days times many jets it adds up to real money.

The 787 does not use engine bleed air to power the air conditioning system at all. Instead the engines have more & bigger electrical generators and some of the extra electricity drives electric motors and air compressors that take ambient outside air & pump it up to cabin pressures & temps. The thinking is the net energy losses from the engine & weight reduction from simplification of systems comes out as a winner with this new approach. It’ll be interesting to see how well this works in practice and whether it becomes the new standard for aircraft design.
Yaw Dampers:
The 757 & 767 have one rudder powered by two hydraulic systems simultaneously. And two yaw dampers in continuous operation. The loss of either or both YD is a non-event. There are no speed or altitude restrictions.

The 737 has one rudder with primary & backup hydraulics. And a primary & backup yaw damper. The only restriction for YD failure is to avoid turbulence and slow down / go down as necessary to get a nice ride if it starts wallowing too badly in the bumps.

The 777 doesn’t have yaw dampers as separate systems. They’re a function wrapped up in the rest of the multiply-redundant fly-by-wire system. The airplane flies OK even with all the FBW smarts off and there are no speed or altitude restrictions. There are warnings about avoiding abrupt control inputs because overall it handles differently (read as “less nicely”) than you’re used to.

The A320 doesn’t have yaw dampers as separate systems. They’re a function wrapped up in the rest of the multiply-redundant fly-by-wire system. The airplane flies OK even with all the FBW smarts off although the checklist says to slow down about 20%, mostly for loss of Vmo/Mmo protection, not specifically for loss of YD. Folks say the airplane is a little twitchy in backup manual mode vice the normal.

The A330 is similar to the 320 but doesn’t even have the speed restriction.

The DC9/MD80 is a much older design and has dual yaw dampers, but only one is active at a time and switchover is manual. No restrictions if both are inop.

I don’t still have the manuals for the 727. But as I recall the loss of one didn’t really change the handling qualities, but required we slow down & go down. I forget the exact numbers but something like max altitude 29,000 & max speed 280 / M0.75. Which is to say maybe 80% of the normal max numbers. The real challenge was if both failed, especially in the original -100 or “stubby” version. That thing really wanted to get divergent if you lost both at high altitude / high speed. We used to practice Dutch roll recovery as a simulator maneuver. It was definitely a scenario where catching it early was the key to recovery. A ham-fist could turn the thing upside down pretty easily. Overall the restrictions with one inop were more about protecting against losing the second one than they were about problems flying on just one.

Bottom line:
My semi-educated guess is that more modern twin engine aircraft are relatively more overpowered than the older 3 and 4-engine jets. As such they have relatively bigger fixed vertical fins to handle the relatively bigger worst-case thrust asymmetry at takeoff power. Which in turn leads to better natural damping at speed / altitude. So the yaw damper has morphed from something needed to make the airplane flyable at all into something that incrementally improves the ride & handling qualities.

573

Thanks guys, that was great for ‘splainin’ for me.

LSL, thanks for the added YD info as all my questions were from 30 years ago or longer and all the new stuff was not on the line yet… I was under the impression that is was a lot more serious…

Old stories I heard back in the late 60’s was that a run a way stabilator on a Falcon 20 was best dealt with first with a 90° bank and then you had time to start thinking and looking at stuff… ??

I was taught how to fly VOR with a broken needle. …

All kinds of obsolete info in today’s world of flight.

Have been seeing the picture of the B-52 that lost the vertical fin a lot on the internet & so I am curious if that was really a big deal as far as Dutch Roll would be concerned?

574

As I said, loss of all yaw damping in a 727-100 at high altitude was a handful. More than one airplane fell from the sky that way. I vaguely recall the 707 was similar. So on at least some airplanes it certainly was a pretty big deal back in the Dayes of Yore.

Runaway stabilizer trim will kill a jet very quickly and thoroughly. So there are lots of cutouts and redundancies. Unlike a small airplane the stab’s maneuvering power is far, far greater than the elevator’s. So full nose-up stab and full nose-down elevator nets to massive nose-up control input.

The difference is due to the relatively wide CG range, the huge difference in weights from empty to full, and the swept wings which move the center of lift a bunch depending on speed. Plus just the wide speed range. The end result of all that is the need for a very wide range of high-power pitch trim.

And yes, for nose-up runaways step one is try to stop the runaway and step 2 is bank as necessary to stop the climb. Which may take 60 or more degrees of bank. If you can get the stab back to a better setting you may be able to land. If not, well …

The good news is runaways are very, very rare. Stab inop / stuck is much more common, although it’s still a pretty rare malfunction. Which can also leave you way out of trim for landing, requiring really strong arms (times 4) and a reduced or no-flap very high speed landing to maintain control all the way to touchdown. Did it once for real and don’t want to try it again. It’s also a pretty standard sim training maneuver although it’s normally stuck at a pretty benign setting in the sim.

We used to routinely practice RMI-only VOR approaches in the USAF. And ADF approaches. Haven’t had to do either one in an airliner since the early 1990s. You’re right that some old school stuff is becoming obsolete. I and most of my elder peers have mixed feelings about this. The new stuff has its issues too.

It’s pretty amazing that B-52 survived. AFAIK, most Dutch roll issues are at high altitude and high Mach. As I recall they lost the fin at high speed but relatively low altitude. And promptly slowed down. That’s probably to core of what saved them.

575

Thanks for the info. That fills in some blanks I have/had on this stuff…

Glad some else notices the loss & change in what is important & relative is not always the best stuff to lose.

You have had some adventures in the air and lived. Some call it experience.

Adventure = terror in retrospect … :smiley:

576

Ref the B-52 tail fin event …

Ref Boeing B-52 Stratofortress - Wikipedia there were four B-52 loss of vertical fin events; two in Jan 1963 & two in Jan 1964. Three of these ended in crashes and one landed successfully.

See also 1963 Elephant Mountain B-52 crash - Wikipedia and 1964 Savage Mountain B-52 crash - Wikipedia for more details on two of the accidents and the research efforts in the investigation.

577

It sounded to me like the 4th one WAS the research into the problem. They were deliberately flying into difficult winds.

578

In 1961 I was around a hanger a lot that had an air force sheet metal guy who said he had to patch cracks in B-52 rear sections ( ? ) that were many times 12 inches long after nearly EVERY flight. His area that he specialized in?? He said in the or on the tail ( vertical stabilizer ) too.

We thought he was just blowing smoke at the time.

Maybe he was being truthful…

579

I just came across the first passenger carrying quadcopter drone – the Ehang 184. It’s apparently already flying and has flown with a passenger. Technically, I suppose it’s a octo-copter, as each strut has two props for redundancy in case of one failing. You can find some other links as well – it’s making appearances now at consumer electronics shows.

It seems the plans are to introduce it in China first, and then the US. I very much doubt it will ever be certified, and I personally wouldn’t go further than a takeoff and landing in the same spot. All kinds of issues – the main one being no flight controls whatsoever. It’s controlled by a phone app or an onboard tablet, and all you can do with the tablet is to pick a destination on a map and hit the “take off” button. Its range is limited to just about 10 miles, less than 25 minutes of flight time, and yet they’re claiming "short to medium distance range. Since each pair of rotors are just a couple of inches apart, you’d have to assume that something like a bird strike would take out both propellers. Oh, and cost is expected to be 2-3 hundred thousand dollars.

Interesting, though. I could see some future version of this being some kind of emergency vehicle for escape, or supply delivery, though I’d imagine it would need at least 10 times the range to be of much use in that capacity.

580

My new hoodie arrived in the mail yesterday. It says ‘All I care about is flying… and like maybe 3 people. (And beer)’