Reply
 
Thread Tools Search this Thread Display Modes
 
Old 03-19-2019, 12:50 PM   #121
Guru
 
Seevee's Avatar
 
City: st pete
Country: usa
Vessel Model: 400 Mainship
Join Date: Sep 2016
Posts: 1,980
Quote:
Originally Posted by ssobol View Post
That might depend a bit on the initiative of the pilots involved. Some only learn what is actively taught to them (i.e. spoon fed), others are actually interested in how the thing works and spend the time and effort to learn as much as they can about it. Since an airplane works in an environment that will kill you if you mess up, you'd think pilots would want to know as much as possible about their plane and how to operate it.

Before someone points out that the MCAS may not have been adequately explained in the pilot's manual, there are other sources of information about the aircraft systems (e.g. aircraft maintenance manuals).

Sort of like people and cars. Some have an active interest in how the car actually works and others think of it as an appliance. Turn it on and it works, if it doesn't call somebody.
Ssobol,

True, some have different levels of initiative. I'd bet that most of the members on TF get fairly actively involved in the mechanics of their boats and how they work. Wonder if the same enthusiasm is at the 100 ton Captain's level, where they're hired to run the boat.... probably similar to the pilots that fly for airlines.

Over my career as an airline pilot, most of us had an interest in knowing beyond what the book said, and a lot were active general aviation pilots, too. And we loved our jobs.

There were a few that just couldn't wait to get off the plane, get out of training and wouldn't put a dimes worth of effort into knowing more than how to cash their paycheck. And they were not fun to fly with. Suspect similar in boating.

I went all the way. Even got a mechanics license with inspection authorization. I want to know what makes it tick. However, even though I was legally rated, I could even change a light bulb for the airline I worked for. One time, they hired a mechanic to drive over from a neighboring airport to change a nav light that I couldn't touch. Took a few hours.... 10 min job, 10 min to sign it off, and 2 hours in driving. Go figure.
__________________
Advertisement

__________________
Seevee
Seevee is offline   Reply With Quote
Old 03-19-2019, 01:05 PM   #122
Guru
 
ssobol's Avatar
 
City: Leesburg, VA
Country: United States
Join Date: Mar 2015
Posts: 570
Quote:
Originally Posted by Seevee View Post
...
I went all the way. Even got a mechanics license with inspection authorization. I want to know what makes it tick. However, even though I was legally rated, I could even change a light bulb for the airline I worked for. One time, they hired a mechanic to drive over from a neighboring airport to change a nav light that I couldn't touch. Took a few hours.... 10 min job, 10 min to sign it off, and 2 hours in driving. Go figure.
Might've been more of a union issue than anything else (both the pilot's AND mechanic's).
__________________

ssobol is offline   Reply With Quote
Old 03-20-2019, 05:41 AM   #123
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 18,774
"The data indicated the nose-down yoke forces peaked at a little more than 100 pounds. "

100lbs is no big deal. Early Soviet aircraft had no hydraulic boost systems a 100 lbs on landing flair was fairly common, both drivers pulled. Of course the Soviets were used to the need for brute force.

"You're right about pilots should be able to handle unexpected/unusual actions but only to the point where they have been trained. If the news is correct, that the pilots where not only NOT trained, and they didn't know this existed, then they should be totally innocent."

"Runaway trim" procedure is taught for every aircraft that has a system.
FF is offline   Reply With Quote
Old 03-20-2019, 08:21 AM   #124
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 4,913
Ok, non pilot here, with a question. I'm confused by the term "trim". I understand the whole elevator can be rotated around it's axis by the jackscrew machine. Also, on the end of the elevator are smaller movable surfaces that I would call "trim tabs".

So is "runaway trim" when the jackscrew drives the whole elevator uncommanded, or does it involve the smaller tabs?

I think pulling the yoke operates the jackscrew, and the little wheels control the tabs? What is the purpose of the tabs?

I know on smaller aircraft the horizontal stabilizer is fixed and the elevator is the movable tabs on the aft of the stabilizer. On large aircraft the whole stab moves, but still has tabs on the end. Not super clear what the tabs do, just neutralize aero force on the jackscrew?
Ski in NC is online now   Reply With Quote
Old 03-20-2019, 09:42 AM   #125
Grand Vizier
 
Delfin's Avatar
 
Join Date: Jan 2010
Posts: 3,398
Quote:
Originally Posted by Ski in NC View Post
Ok, non pilot here, with a question. I'm confused by the term "trim". I understand the whole elevator can be rotated around it's axis by the jackscrew machine. Also, on the end of the elevator are smaller movable surfaces that I would call "trim tabs".

So is "runaway trim" when the jackscrew drives the whole elevator uncommanded, or does it involve the smaller tabs?

I think pulling the yoke operates the jackscrew, and the little wheels control the tabs? What is the purpose of the tabs?

I know on smaller aircraft the horizontal stabilizer is fixed and the elevator is the movable tabs on the aft of the stabilizer. On large aircraft the whole stab moves, but still has tabs on the end. Not super clear what the tabs do, just neutralize aero force on the jackscrew?
Trim tabs on a plane so the same thing that they do in a boat - dial in the fore and aft orientation to the direction of travel, compensating for variable weight distribution so straight and level flight is attained without as much pilot involvement. The autopilot, if capable, is constantly moving the trim tabs to maintain a selected altitude. When two ton Tessie gets up from 34A to go forward to use the first class head, the trim tabs compensate for the change in weight distribution.

If there is a system malfunction and the plane starts to behave in an unexpected way, the first response of the pilot would generally be to disengage all auto flight gear and take control of the aircraft.
Delfin is offline   Reply With Quote
Old 03-20-2019, 10:06 AM   #126
Guru
 
Seevee's Avatar
 
City: st pete
Country: usa
Vessel Model: 400 Mainship
Join Date: Sep 2016
Posts: 1,980
Delfin,

Good explanation, and here's a picture to make it a bit more clear....

The elevator moves when the pilot pulls or pushes on the control yolk.
The trim tab moves when the pilot turns the trim wheel.

The trim tab is to take out any force needed on the elevator to maintain the desired flight path. So, when properly trimmed, the pilot can take his hands off the control wheel without any change in pitch.... plane flies in trim.

Now, there are some planes, like the 737, where the stabilizer moves to trim the plane, so there's no trim tab. And the stabilizer is moved by the jack screw.
Accomplished the same thing, but a bit more aerodynamically clean.

Now enter the autopilot, which can control all of the above. In fact the autopilot can fly the plane from just after takeoff to a full stop landing at destination. The autopilot is not certified for takeoff or taxi, which must be done manually.

Now enter electric trim, which can be controlled by the pilot when hand flying or by the autopilot to keep the plane in trim.

Now enter MCAS, to supplement the controls/trim for a poor design above. A band aid.
Attached Thumbnails
Click image for larger version

Name:	Trim-tab.jpg
Views:	28
Size:	28.2 KB
ID:	86559  
__________________
Seevee
Seevee is offline   Reply With Quote
Old 03-20-2019, 10:09 AM   #127
Guru
 
Seevee's Avatar
 
City: st pete
Country: usa
Vessel Model: 400 Mainship
Join Date: Sep 2016
Posts: 1,980
Quote:
Originally Posted by ssobol View Post
Might've been more of a union issue than anything else (both the pilot's AND mechanic's).
Good point, but not the issue at "away" stations where the mechanic is most likely non union and only needed for minor repairs that happen there, or on the inbound flight.

For a major issue, most companies will rent a small jet and bring their own mechanics to fix things. That's probably going to happen in places where their 737 Max got stuck, if they couldn't get a ferry permit to bring it home.
__________________
Seevee
Seevee is offline   Reply With Quote
Old 03-20-2019, 10:10 AM   #128
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 4,913
But that image is not what is on an airliner. The whole horizontal stabilizer moves, not just the elevator panels shown and trim tabs (??).
Ski in NC is online now   Reply With Quote
Old 03-20-2019, 10:19 AM   #129
Guru
 
twistedtree's Avatar
 
City: Gloucester, MA
Country: USA
Join Date: Jan 2013
Posts: 4,525
Quote:
Originally Posted by Ski in NC View Post
But that image is not what is on an airliner. The whole horizontal stabilizer moves, not just the elevator panels shown and trim tabs (??).

I think that's what SeeVee was describing 4th paragraph? So variation in plane designs.
__________________
www.MVTanglewood.com
twistedtree is offline   Reply With Quote
Old 03-20-2019, 10:54 AM   #130
Guru
 
Xsbank's Avatar
 
City: Pender Harbour, BC
Country: Canada
Vessel Name: Gwaii Haanas
Vessel Model: Vancouver Shipyards Custom Aluminum 52
Join Date: Sep 2013
Posts: 3,103
I’ll try... There are three motions observable on an airplane, pitch, roll and yaw. All of these are controlled by the pilot to make the aircraft perform the desired movement and all of these forces have aerodynamic surfaces that can be moved to achieve the desired result. They all work the same way by moving a surface against the airflow to deflect the lifting surface (wing) in such a way to influence lift.

The so-called tail of the aircraft does not carry any of the weight of the aircraft, its purpose is to influence the pitch, or the angle of attack of the wing, which does carry all the weight. The rudder is there to control yaw and only in certain circumstances (landing in a crosswind, for example) is it actively used, in flight the computer operates it automatically, calling it a “yaw damper.”

Pitch, the one we are discussing, is controlled by the elevator whose motion is controlled electrically, hydraulically or by cables by the pilot pulling or pushing on his control column. Most modern aircraft have hydraulically actuated rams which are controlled electrically through the assistance of a computer. The amount of force required to deflect a large surface like an elevator against the airflow is high, hence the hydraulics (or “boosted controls”).

If you can picture the forces required to deflect these surfaces and think of how long they might need to stay in the same relative deflection, for example a climb or descent, devices called “trims” are installed to help the pilot. For example, If a climb from take-off to cruise elevation is desired, the pilot pulls on the column and without a trim, holds that back pressure. And holds it and holds it, using the force to deflect the elevator. As you might imagine, this is fatiguing and difficult to be smooth for the hour or so that this might take so for passenger and pilot comfort, trim systems are added. As the main control is deflected, the pilot can move a trim, either mechanically through a wheel and cables or electrically. In the case of a modern aircraft, the entire horizontal stabilizer can be adjusted into the airflow electrically by moving a jackscrew that moves the horizontal, “ not moving” surface. This effectively takes the force off of the pilot’s column and keeps it centred, taking the strain off the pilot so he can relax and the aircraft keeps the same climbing attitude with the control column neutral.

In practice, the pitch trim is continuously being moved. The rudder trim, however, is usually set once and forgotten, the yaw damper (part of the autopilot) controls the rudder. Same with the aileron trim, it is set so that the aircraft returns to wings-level when the column is released after a turn and is rarely adjusted.

The trim is a powerful tool and on those aircraft that use them, small surfaces attached to the trailing edge of the elevator can be moved against the airflow to deflect the elevator. This is the method most small or older aircraft use although a Cessna 185 trims its horizontal stabilizer with a jackscrew...On some older larger aircraft, like a DC6b, the elevator was not connected to the pilot’s control wheel at all, it was free-floating and trailed in the airstream. The pilot’s control wheel was attached directly to the trim surface which moved and deflected the elevator to control pitch. I found that difficult to comprehend when I first encountered it, but it works fine.

Most well-designed aircraft, particularly those that carry passengers, are stable. That means they fly neutrally with little input from the pilot, tending to just cruise like a car on the freeway. Any deflection from stable flight means the aircraft returns naturally to stable flight condition. Conversely, a fighter is designed to have little or no stability, its ability to maneuver depends upon it. If a gust hit a fighter and the pilot did nothing, it would not return to stable flight on its own. Events like winds, power changes, flap deflection or landing gear movement up or down can affect stability such that aircraft have to compensate for these changes and usually a control deflection of some sort, perhaps accompanied by trim is required. In most cases, the autopilot does all this. Modern aircraft are almost exclusively flown by the autopilot and/or a computer except the final stages of landing, ground maneuvers and takeoff. Passenger comfort demands this.

Sometimes these automatic systems (or any other systems) fail which is, in modern times, the primary purpose of the crew still being up there (and to get the aircraft to the terminal, still done manually). Because aircraft are very complex now, pilots go back to school every 6 months to get more training and to re-qualify. In addition, authorities require that you have to do a minimum of 6 take-offs and landings before you qualify to fly the aircraft each 6 months.

In North America and Europe, pilots had a long apprenticeship in small aircraft before they were qualified for larger airlines; it was a process of flying larger and more complicated aircraft and progression was slow and many pilots might not get to be an airline captain until the later half of their careers. This meant that captains had huge experience and were very well trained in multiple aircraft types. When things went wrong, pilots like Sulley used their vast experience because there was no direct specific training to save the day. Recurrent training is designed to expose the pilots to all of the emergencies he might face, or have been faced, by other pilots.

Nowadays, low-cost airlines, airline failures and many start-ups, low wages coupled with difficult working conditions means that fewer people are willing to be pilots - there is a current world-wide shortage and many captains got to their positions without the long apprenticeship programs. A captain by age 28 was unprecedented in my day. New pilots must be excellent systems managers and most are but many do not have the fundamental flying skills, that old “stick and rudder” stuff to fall back on. Add long flying legs with the autopilot engaged and one landing at the destination and there is very little hand flying done. I have trained new pilots who were amazing on the computers, much faster than I would ever be, but few, if any, knew what the rudder was for.

Times change.

Sorry, this is obviously redundant, took too long to write and I was undercut. Good work guys!
__________________
Don't believe everything that you think.
What are we offended about today?
Xsbank is offline   Reply With Quote
Old 03-20-2019, 11:10 AM   #131
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 4,913
Thanks, Xs.
Ski in NC is online now   Reply With Quote
Old 03-20-2019, 11:59 AM   #132
Guru
 
ssobol's Avatar
 
City: Leesburg, VA
Country: United States
Join Date: Mar 2015
Posts: 570
Quote:
Originally Posted by Xsbank View Post
... Recurrent training is designed to expose the pilots to all of the emergencies he might face, or have been faced, by other pilots.
...
The only thing about recurrent training is the time does not allow training in "all of the emergencies he might face" each time a pilot goes for recurrent training. The more common or most critical emergencies get more attention (e.g. engine failure), others issues are trained less often. For a pilot to see all of the emergencies would require a number of years of recurrent training.

However, I'm sure that trim issues are now going to be much more prevalent in 737 MAX training (initial and recurrent) for the next several years.
ssobol is offline   Reply With Quote
Old 03-20-2019, 02:17 PM   #133
Guru
 
Woodland Hills's Avatar
 
City: Jacksonville
Country: USA
Vessel Name: Alzero
Vessel Model: Hatteras 63' CPMY
Join Date: Apr 2017
Posts: 668
Stepping back to see the big picture: Ethiopia(!) decided to send the CVR and FDR (black boxes) to France for analysis instead of to America because they did not trust the FAA and Boeing. This is huge!

I assume that this lack of trust took years to develop and it took a major accident for the rest of us to learn about. I guess the days of the US being a leader in aviation are ending, not over technology, but over ethics and the perception of bias.
Woodland Hills is offline   Reply With Quote
Old 03-20-2019, 02:32 PM   #134
Guru
 
ssobol's Avatar
 
City: Leesburg, VA
Country: United States
Join Date: Mar 2015
Posts: 570
Quote:
Originally Posted by Woodland Hills View Post
... the days of the US being a leader in aviation are ending, not over technology, but over ethics and the perception of bias.
Most probably a lack of funding for the FAA that required them to outsource a lot of the things they are supposed to be doing led down a slippery slope that got us to where we are today.
ssobol is offline   Reply With Quote
Old 03-20-2019, 02:46 PM   #135
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 18,666
Or Airbus made things happen behind the scenes instead of the FAA and Boeing.
psneeld is offline   Reply With Quote
Old 03-20-2019, 04:15 PM   #136
Guru
 
Woodland Hills's Avatar
 
City: Jacksonville
Country: USA
Vessel Name: Alzero
Vessel Model: Hatteras 63' CPMY
Join Date: Apr 2017
Posts: 668
I thought Ethiopia was a Boeing airline? Surely there were already tech reps and other Boeing personnel on site from the beginning to consult and advise. Particularly with such a new aircraft. The fact that they still went to France is thus significant.

Allowing Boeing to self-certify using staff on their own payroll could very well have contributed to the crash, but that has nothing to do with foreign airlines thinking that the FAA is biased towards Boeing. They get that from the way FAA handled this affair from the very beginning. Staffing the government with ex-Boeing employees did not help either. Having Boeing and FAA issue nearly identical press releases declaring the plane safe to fly was also a factor in the perception of bias in favor of sales over safety.
Woodland Hills is offline   Reply With Quote
Old 03-20-2019, 04:19 PM   #137
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 4,913
Quote:
Originally Posted by Woodland Hills View Post
Stepping back to see the big picture: Ethiopia(!) decided to send the CVR and FDR (black boxes) to France for analysis instead of to America because they did not trust the FAA and Boeing. This is huge!

I assume that this lack of trust took years to develop and it took a major accident for the rest of us to learn about. I guess the days of the US being a leader in aviation are ending, not over technology, but over ethics and the perception of bias.
I don't see it as dark as that. I do failure analyses as part of my business (certainly nothing related to aero). You want to consider whether there is any potential "conflict of interest" when you arrange parties to do an analysis. There is potential for such a conflict with at least Boeing in this incident. I see nothing out of sorts about having the French take the lead.

The Ethiopians did trust Boeing enough to buy their aircraft.
Ski in NC is online now   Reply With Quote
Old 03-20-2019, 04:35 PM   #138
Senior Member
 
Boat's Avatar
 
City: SchoolHouse Branch
Country: USA
Join Date: Jul 2018
Posts: 283
Some of this doesn't pass a smell test. The idea that unless the pilots turned off the automated systems the Max would crash itself, Boeing knew, and chose to do nothing about it. There's gotta be more to this story.

Quote:
Originally Posted by ssobol View Post
That might depend a bit on the initiative of the pilots involved. Some only learn what is actively taught to them (i.e. spoon fed), others are actually interested in how the thing works and spend the time and effort to learn as much as they can about it.
I promise you that this is true of many, many software development people.
Boat is offline   Reply With Quote
Old 03-20-2019, 04:43 PM   #139
Guru
 
AlaskaProf's Avatar
 
City: Tacoma, WA & Ashland, OR
Country: US of A
Vessel Name: SEEADLER
Vessel Model: RAWSON 41
Join Date: Jun 2016
Posts: 785
Quote:
Originally Posted by Ski in NC View Post
But that image is not what is on an airliner. The whole horizontal stabilizer moves, not just the elevator panels shown and trim tabs (??).

Yes it is called a stabilator and I believe the above reference to a jackscrew which moves it is misleading. The MD 80 for example works that way. On the 737, the control inputs from the yoke or the autopilot go to the trim tab which basically exerts an aerodynamic force shoving the freely swiveling stabilator where you want it.


Then a small "trim jackscrew" balances the forces so the system achieves a new stable state. This is the bit which was found set "full nose down".
AlaskaProf is offline   Reply With Quote
Old 03-20-2019, 05:20 PM   #140
Member
 
City: Victoria BC
Country: Canada
Vessel Name: Tiffany
Vessel Model: Apollo 32
Join Date: Jun 2018
Posts: 10
Interesting discussion on the topic with a 20 year 737 pilot (also flew 737 Max) at my North Saanich marina: "Pilots rely on too much automation (ie; auto pilot with trim tabs)". When things begin to go sideways switch off the automatic functions. The auto nose down MACS system was introduced with little-to-no training or notification. Shutting down the autopilot function should have been their first reaction to an out-of-order flight situation. Fly the plane.
__________________

Tiffany is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 07:19 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012