Common misunderstandings B737
 

G'day,
I am not a Training Captain.
I would like to ask all you Checkies and Trainers out there on the B737 series (or other types if it applies to jets in general) what the most common misunderstandings are that you come across either in the sim or on line checks.
I'l give you an example, many of the pilots I fly with don't understand the basics of how the cost index system works.
What are some of the common misunderstandings you see year in year out?
Cheers, Framer

Immediate rush to select start switches to CONT in slight turbulence. Using autobrake when runway length and surface conditions obviously don't require immediate braking on touch down.
Relying on the cabin altitude warning at 10,000 ft (if not pressurising after take off) rather than checking the cabin rate of climb indicator to confirm pressurisation is taking place normally with this check being done as part of the after take off scan.

On hearing the 60 knot call by the PM during landing, lowering the reverse levers full down quickly causing aircraft acceleration as the reverser panels close leaving the N1 passing 60% on the way down to idle. Failure to read the FCTM which discusses the correct method of going to idle reverse.

Relying heavily on using Supplementary Procedures section to remind pilot how to crossfeed and how to do the necessary switching for engine bleeds off take off and switching to normal bleed config after take off. This is elementary systems knowledge and should be known without resorting to a `cheat sheet`.

Using excess control wheel offset for minor crosswinds on take off when no offset is necessary in the first place. Relying blindly on the PM call of "rotate" before commencing rotate instead of rotating at the VR speed on own ASI bugs. "Following" through (pushing) with hand behind thrust levers during other pilots autothrottle take off. Quite unnecessary and annoying to PF and can cause damage to AT clutch system.

Inability to use commonsense in pilot induced oscillation when hand flying on final. Simply relax death grip on controls for less than a second and aircraft takes care of itself.

Being persuaded by twitchy captain that practice manual flying is dangerous even though weather and ATC conditions are ideal.

Questioning every decision by the captain to make a point you are a team and it is your "Right". In other words big noting yourself and scoring points fuels your ego.

Not keeping an eye outside looking for traffic in VFR departures and arrivals but instead keeping heads down and relying 100 percent on TCAS for initial warning. There are many more but other Ppruners will surely add their own.

Thanks A375,
Some good points there, I think I've managed to make most of those mistakes at one point or another and then had them beaten out of me :)
I wonder about the clutch on the A/T system though, is that from the 2,3,4,500's? because I've never heard of it before. Personally I'd never see a reason to push one up unless there was T/L assymetry but often I'l pull some thrust off in the cruise and hold it for a second or two while the A/T is still engaged....poor practice?

Thrust reduction during the flare:

It's apparently a wide spread technique to initiate the thrust reduction at 10 feet or less with the goal of achieving a smooth landing. In my opinion this technique is wrong (and not in line with the FCTM).

In my opinion it's more than often counter productive and the direct result is a firm touchdown. I believe the cause is two fold. First, it's more difficulty to judge the required input to counter the pitch down moment due to the thrust reduction which happens within a relatively short timespan and at the most critical part of the flare, where you want the most precise control. Second, the extra thrust carried causes the speed to be too high (wind correction should be bled off during the flare) and the aircraft to continue flying, which obviously is counter productive as well, when the goal is to land.

Then there is the aspect of flaring distance. The above will certainly result in a landing in the last part of the touchdown zone, and those that regularly uses this technique may do so quite consistently. However, once in a while they have to "drop it", for a very firm touchdown, when it becomes clear that it would otherwise result in a long landing.

With correct technique, it's no problem to close the thrust levers by 30' and obtain a perfectly smooth landing. With the added bonus of being in the beginning of the touchdown zone. Again the reason is two fold and the opposite of above. First, it's easier to adjust the control input required to counter the pitch down. Even if you use either of two techniques: 1) Slowly closing the throttles give more time and better feel to keep nose where it should be. 2) Slamming the throttles shut at 20-30 feet may not give the same accurate feel, but it then gives more time (feet) to get the adjustment right. In any case the adjustment is complete before the final critical few feet of the flare and all control input can be concentrated about path control, instead of thrust compensation, for the most precise control. Second the engines are at idle and the speed is correct and decreasing when touching down - the aircraft is ready to land by itself more of less with very little input.

Of course there are circumstances that may warrant to keep the thrust in or even adding thrust in the flare, likewise sometimes thrust reduction should be initiated higher than 30 feet as well. But either should be done as a deliberate action when required. Reducing by 10 feet as the norm should not.

...and reduce speed to .76 during cruise. Even when there are no recommendations in the manuals to set this speed for cruise phase of flight at any turbulence intensity.

If one knows his C pattern and read the after take off checklist afterwards he is covered.

Are you saying on a normal landing the thrust levers should be closed at 30ft? I reckon I have only seen that done two or three times ever. Would it not increase the chance of either a tail strike or hard landing if you misjudged it?
My thoughts on the Bleeds off take-off; We use a checklist to confirm proceedures that we do every single time we fly, so why would we then decide that after introducing a proceedure used rarely that the checklist is a bad idea?

Yes, that's what I am saying.

Here is what the auto throttle is doing during an autoland for reference:
"the A/T begins retarding thrust at approximately 27 feet RA so as to reach
idle at touchdown. A/T FMA annunciates RETARD."

No, I actually believe that reducing the thrust at 10 feet carries a bigger potential for a tail strike. Typically the tail strike occurs when the pilot gets surprised for whatever reason and pulls back on the controls to and gets a rising radio altitude, speed decaying quickly and pitch rising. Having a nose down moment due to thrust reduction may add to the surprise, especially for the less experienced pilot (add to the situation a dark night, a runway with no centerline lights etc.). Floating is another factor that increases the risk of a tail strike. I believe the scenario is often seen with the 10 feet reduction: RA goes 10, 8, 6, 4, 4, 4, 4... and pitch keeps rising, usually ending with the aircraft falling those last feet for an uncomfortable arrival. I believe this floating is because of the thrust carried into the final part of the flare as written above and/or that a too large input was give to compensate the the falling nose. When a too big input is given, it's difficult to reverse it.

Here is another pitfall mentioned in the FCTM, though I will agree that you have to be really unlucky for this to occur:
On the other hand with reduction at 30 feet, the risk is reduced because the aircraft is not going to float and you are not getting any pitch surprises a few feet off the runway. The only risk of a tail strike, that comes to mind, is when reducing thrust early is combined with what typically is a beginner error in the flare itself. Namely to start raising the nose at 50 feet. With such a misjudgment, as you say, I guess a tail strike is possible with any technique. This often happen because the inexperienced pilot is fixated on the following the FD instead of looking out the window. Upon hearing the 50 call and looking out the window becoming surprised at the rising runway and pulling back the controls. This can be avoided by looking out the window early, preferably the last 2-300 feet, keeping the aim point fixed in the cockpit window and only looking in to check the speed. If the approach was stabile when reaching 300 feet there really shouldn't be much reason to look at the FD or ILS anymore.

After the thrust reduction stop the nose from dropping and not more, which is usually a movement on the control which can be accomplished with the wrist. At 20 feet pull very slightly on the controls to bring the nose up (FCTM says 2-3 degs, I never looked so I can't verify this). After that there is actually not much movement required. At 10 or 5 feet maybe a little after adjustment. But I will claim that from the initial adjustment at 20 feet, without further input a quite acceptable landing can be made, because all parameters (idle thrust, speed, descent rate) are correct. The last adjustment is to get it smooth.

The opposers to reducing the thrust at 30 feet, have a fear that aircraft will drop out of the sky like a stone if thrust is at idle. It will not. My guess is that this idea comes from the feeling of the pitch down when thrust is reduced.

A typical bad flare begins with the a slight break at 50 feet, followed by another one at 30, thrust reduction at 10 feet, a touch down zone drifting hasty by below and a drop from 4 feet to avoid entering the FOQA statistics for long landings.

A good flare is thrust to idle at 30-20 feet, keeping the nose from dropping, almost simultaneously lift the nose the notch that the FCTM describes as 2-3 degs at 20 feet and another notch at 10 to 5 feet. Result a nice smooth touchdown in the beginning of the touchdown zone. :)

Assuming a -700 landing at flaps 30 the normal pitch is 2.5 degs on the 3 deg ILS. If we take the high value 3 deg pitch up at 20 feet from the FCTM and add another highly set 2 degs for the extra notch at 5 feet, we get 2.5 + 3 + 2 = 7.5 degs pitch. Tail strike occurs at more than 12 degs with compressed struts.

Had an F/O do this to me once after climbing out of fog after take-off. It certainly got my attention!

I have to agree with all of what A37575 has to say, particularly not checking the cabin is pressurizing during the climb before reaching 10,000', stowing the reversers fully at 60 kts & getting a burst of forward thrust & waiting for the "rotate" call instead of rotating on your own ASI & using the call as a back up as per the FCTM.

As for landing, cosmo kramer is correct. Start reducing power to idle at 20 -30 feet & then flare the thing, instead of flying it on with a nose low attitude. Works nicely with flap 40 as well!

Absolutely agree with that!

Works well for me to use the FCTM method :D

Here is the list so far of

"Stuff that annoys your friendly checkie"

1/Start witches to Cont in light turbulence
2/ Using Auto Brake when it's not needed
3/ Not checking the cabin ROC indicator with the ATO cx's
4/ Quickly stowing the reversers at 60kts
5/ Using Sups for crossfeeding and No Bleed takeoff
6/Using too much aileron during roll during crosswinds departures
7/Relying blindly on the rotate call
8/Following through on thrust levers after TOGA pushed
9/Inability to resolve PIO's
10/ Thinking that hand flying is dangerous
11/Questioning every decision the Captain makes
12/ Relying 100% on TCAS instead of looking out
12/Reducing to M0.76 in the cruise due turbulence
13/Maintaining thrust until 10ft during flare

Lets see if we can get it to the
"100 things that annoy your friendly checkie".

One thing from this I am interested in finding out, if we are in the cruise and the speed is sitting a few knots high and the A/T is doing nothing about it, and I take 1% off the N1's by pulling the thrust levers back for a few seconds, can that cause damage to the motors and clutch ? I have never heard it mentioned before and thought the machine was designed to do that.
Framer

On the -300 the configuration of the bleed panel was the V or C however on the -800 it was always a checklist which I must say I prefered.

Not confirming the FMA(s) always got me adgitated, especially when someone would comment "whats it doing" or would be in HDG instead of LNAV etc.

Not checking Cabin ROC - unacceptable.

Using checklists/handy dandies to cover the windows because of the sunlight. You obviously couldn't see out the windows and it totally ruined the checklists.

Over controlling on the approach (PIO) and you ended up doing this little "jig". The pilot would probably be thinking it is the atmospheric conditions.

Slow rotation, not pulling correctly through the dead zone thus increasing likelihood of a tail strike, not pulling to correct pitch attitude or following FD's to above 20 degrees.

Basically not reading the books and poor airmanship irritated me, and the blank look when you are politely trying to point this out.

"Stuff that annoys your friendly checkie"

1/Start witches to Cont in light turbulence
2/ Using Auto Brake when it's not needed
3/ Not checking the cabin ROC indicator with the ATO cx's
4/ Quickly stowing the reversers at 60kts
5/ Using Sups for crossfeeding and No Bleed takeoff
6/Using too much aileron during roll during crosswinds departures
7/Relying blindly on the rotate call
8/Following through on thrust levers after TOGA pushed
9/Inability to resolve PIO's
10/ Thinking that hand flying is dangerous
11/Questioning every decision the Captain makes
12/ Relying 100% on TCAS instead of looking out
12/Reducing to M0.76 in the cruise due turbulence
13/Maintaining thrust until 10ft during flare
14/Not confirming the FMA(s)
15/Using checklists etc to cover the windows (sunlight)
16/Over controlling on the approach (PIO)
17/Slow rotation, not pulling correctly through the dead zone

Good stuff Eagerbeaver, question....what about blocking out the sun during the cruise, for me, with TCAS etc, I figure it's safer not to be uncomfortabe and maybe even get a headache...acceptable?

I know, it is picky and it is extremely bright during the day. The sun visors are inadequate. I used to put up with it.

http://www.pprune.org/data:image/png...BJRU5ErkJggg==
Boeing AFM:

Where do you think they came up with those FMC numbers?

If you're climbing or descending, you pitch for speed. In "level" flight where the jet is being shaken, you need a target N1 to get the target speed. The speed is the goal, not the N1. And that goal doesn't change whether you're going up, down, or level.

How about, when switching frequencies, they immediately start transmitting, without pausing to see if there is already a conversation in progress?

Yes if the FMC is inoperative you should use the target N1 for unreliable airspeed for .76 cruise. But I disagree that the target is to obtain that particular speed, the goal is to provide provide high high/low speed margin. If the result is .79 that's fine too:
Hence, if the result is .79 you should only reduce thrust if having a large increasing trend vector.

Anyway, that was not the point.

The point was that some people blindly sets this speed without knowing what they are trying to accomplish. It's not some magical speed that will provide a smoother ride, which people seems to believe when selecting it during light turbulence.

Find it quite amusing that this thread is entitled "Common Misunderstandings" and yet you cannot agree amongst yourselves!

Maybe it would be better to title it "Training system fails to get the correct message across?"

Pot calling the kettle black?

- err - those two don't quite join up! Is M.65 acceptable? M.82? As long as you have the right N1's of course......................

NB For youngsters - N1's do NOT provide buffet boundaries.

- Late descent clearence for some reason - pushing LVL CHG and pulling the thrust levers back manually without waiting for the AT to do it - of course speed will decrease below the target - leads to nice oscillations during the first couple thousand feet - after this, complaining how unreliable the AP is as it fails to maintain speed.

- Starting the descend 20NM before the TOD because "the -200 had a bad press. system, and it needs time to sort out the descend rate."

- Putting the automatic temperature selector to full low (or even to manual) on a hot summer day (same on the Airbus). It sets temperature, not the rate of cooling!

-Doing the flight control check (rudder part) without holding the tiller, or with a speed you have hard time following the yoke.

-Disregarding a gentle suggestion by the FO not to climb to the max level when it is turbulent and it was turbulent on the other way 2 hours ago - almost stalling -then explaining why it was a dangerous. (as the 700 was really unstable on the speed during turbulence)

-When "Drag Required", pulling the speed brakes, even as PM, although we still have 70 NM, no wind and we are at FL200 at 270kts with no descend restriction, then explaining, during the 15 NM level flight, what drag required means (descend planning is quite easy on the classic, the second part is mainly CRM, I admit)

-Taxiing with 15 its on a long strait taxiway and when the whole airplane starts vibrating at 16 kts, slowing down to 14, which does not solve anything, and after this, writing it down to the tech log as a failure (I might not be correct about the exact speeds, but there is a note in the FCTM about this)

- 737-300, 16 NM on the LOC/GS, Flaps 5, 10 kts headwind, speed around 15-20 kts higher than the bug, very slow but steady deceleration, no speed restriction. AT warning light starts to flash, PM (usually the CDR), either puts the gear down or extends the speed brakes. (not because of the circumstances, but because he/she does not understand what the three lights next to the PFD mean (which I also forgot by now))