Ace the technical pilot interview.
 

Seems many people who are preparing for their CX interview have bought ”Ace the technical pilot interview” (myself included). I like the idea of the book and I did find it quite useful when preparing for the first interview.

But, as has been mentioned on the forum before – there seem to be many errors in the book. I was thinking that we could try to list the questions that SEEM to be wrong and have a discussion about them.

I have the e-book version, but I think the pages would be the same in the printed version. Since I don’t know how much interest there is for this post I will just start from the beginning of the book with the first errors I have found, and list more if someone replies.

Some of the answers I have marked down are probably correct in the book, and the error is on my part not having understood it. To be honest, it just seems unlikely that they would publish it if all the answers I found strange/incorrect were in fact not right

Page 4. –What is the formula for lift:
"½R+V²+S+CL"
(+ instead of *) - embarrassing!

Page 13 - How is the pitching moment of the lift-weight couple balanced?
"Lift forward of weight has a nose-up pitching moment, which is counterbalanced by the downward deflection of the horizontal tailplane, which creates a nose-down counterpitch. Therefore, lift aft of weight requires the opposite balance."
Other way around, no?

Page 31 - What causes Dutch roll?
...a marked bank occurs to the point where the outer, upward-moving wing stalls and loses all lift, and therefore the wing drops, causing a yaw to the stalled wing and thus leading to the sequence being repeated in the opposite direction.
Im not sure about this one, but would the upward-moving wing generally stall?

Page 40 - What are the effects of extending flaps in flight?
Lowering the flaps in flight generally will cause a change in the pitching moment. The direction and degree of the change in pitch depend on the relative original position of the center of pressure and the center of gravity.

The factors that contribute to this are
...
3. The flaps will cause an increase in the downwash, and this will reduce the angle of attack of the tailplane, giving a nose-up
moment.
If the tail is considered to produce "negative" lift, wouldnt an increased downwash INCREASE the AOA, giving a nose-up moment?

Page 60 - How does a crosswind affect the critical engine?
A crosswind, depending on its direction, can either help to restore or aggravate the yawing moment of an aircraft with a failed critical engine. For instance, a failed critical number 1 engine will cause a yaw to the left. A crosswind component from the left will apply a restoring force to the aircraft’s fuselage, whereas a crosswind from the right will aggravate the yawing moment further to the left due to the sideways force experienced on the right side of the aircraft’s fuselage (which is from the right to the left). Therefore, a crosswind landing is of even greater importance with a critical engine failure.
Other way around again, no?

yep the upward-moving wing stalls and when it does it drops while the other wing hasn't stalled, till the point the unstalled wing is now higher and going into a stall itself, the origianlly stalled wing is now low enough hence its repeating it self again

is the way to fix it by using rudder pedals for secondary affects? since the ailerons are ineffective in any stall situations?

i think its trying to say lift thats foward of the center of weight, that would have a nose-up pitching tendency so its correct saying a downward deflcection of the tailplane would counterpitch

i don't see much problem in that, using the crosswind to balance the yaw created by the critical engine seems logical thing to do, but i would've through upon reaching glide slope you'll just shut down the remaining engine(s) for a glide approach

sometimes these questions gets confusing, especially if you do too much in the one day :) have some rest, and read it again, if it still doesn't make sense read another book to confirm or find info on the issue online

edited, couldn't spell "lift" properly, had "life" lol

You need to get a copy of "Handling the Big Jets" or some ATPL notes and have a read in them on Dutch Roll. To link the upper wing stalling and Dutch Roll is contrary to many other texts that I have read. Yes the angle of attack and corresponding lift production has changed between the wings however to describe it as a stall is a little extreme.

If you can't get hold suitable texts try doing a search of the Tech Log forum as there as been suitable discussions on this sort of topic in that forum before.

FlyingMoggy2,

Rubbish mate. VR-HDB is absolutely correct with their concerns about the inaccuracies with the book. I too had similar concerns about the facts. I merely used the book in order to prepare a well-worded reply for the concepts which I knew too be correct.

For a start, Dutch roll has absolutely nothing to do with a stalled wing. A stalled wing will in fact continue to roll and will not in fact lead to the oscilliatory roll (yaw) tendancies. It is more the relationship between the lag between roll and yaw. The initial yaw (so why is it called dutch roll then :-).....) causes a roll which then causes adverse yaw which causes roll in the opposite direction which again causes adverse yaw......and so on.

A crosswind from the left will hinder the recovery of a No1 eng failure (in conventinal aircraft).

There are more non-truths in the book but I didn't document them so Truckmasters is correct, get Handling the big jets and enough medication to be able to get through the book with sanity intact.

Stick

What garbage. Dutch roll happens when the aircraft has relatively strong static lateral stability (usually due to the swept wings) and somewhat weak directional stability (relatively.) In a Dutch roll the aircraft begins to yaw due to a gust or other input. The yaw is slow damping out so the aircraft begins to roll before the yaw is stopped (due to the increased speed of the advancing wing and the increased lift due to the swept wing effect.)

By the time the yaw stops and begins to swing back toward zero slip the aircraft has developed a considerable roll rate and due to momentum plus the slip angle the aircraft continues to roll even once the nose has begun returning to the original slip angle.

Eventually the yaw overshoots the zero slip angle causing the wings to begin rolling back in the opposite direction.

The whole procedure repeats, sometimes with large motions, sometimes with just a small churning motion. Like all dynamic stability problems, Dutch roll is much worse at high altitudes where the air is less dense.

Dutch roll is almost certain to happen in a jet aircraft if the Yaw dampener is turned off at high altitude. Therefore, the first thing to check if an aircraft begins to exhibit Dutch roll is that the Yaw Dampener is on. The pilot should then try to minimize the yawing oscillations by blocking the rudder pedals (i.e. hold the rudder pedals in the neutral position.) Next apply aileron (spoiler) control opposite to the roll. The best technique to use is short jabs of ailerons applied opposite to the roll. Try to give one quick jab on each cycle (i.e. turn the wheel toward the rising wing, then return it to neutral.) Finally accelerate to a higher speed, where directional stability will be better, or descend into more dense air, for the same reason.

heres a nice read on dutch roll

http://www.av8n.com/how/htm/equilib.html#sec-dutch-roll

sorry bout that wing doesn't stall when it goes up, but the wing does go up and down, i was thinking about stalling in a turn where the higher wing stalls and drops ^^

well the book does say for instance if the crit engine fail causes a yaw to the left, conventional or not thats just an example, a crosswind from the left will help balance a yaw to left no?

FlyingMoggy2

Personally I think it is sloppy teaching to try and explain what is happening to the “Deflection” of the air. It is much clearer to talk about the resultant force. In this case if you had the center of lift ahead of the center of gravity, the coupling of these two resultant force would require a tail up force to balance them out. If the lift and weight is the other way around, you would require a tail down force. Pretty simple really.
I have highlighted the word “from” for a good reason. If it said “to” it would be correct. I’m not sure if it is a typo but it is clearly wrong. A crosswind from the same direction as an engine that has failed is going to make the yaw worse, period. Think about a crosswind take off and the rudder input that is required to keep it straight. Now imagine an engine failing and what effect this will have.

sorry i'm a bit confused now. when you take off into cross wind from the left don't you apply left rudder to keep the plane lined on the run way? if the left engine suddenly failed wouldn't there be a tendency to yaw left? but since left rudder was being applied during take off i was thinking releasing the rudder should allow the cross wind from the left to help balance the yaw a bit?

FlyingMoggy2
No, a crosswind from the left will cause the aircraft to weathercock into wind i.e. yaw to the left or into wind. This is because the fin is being pushed to the right. An engine failure on the left will only make it worse.

i understand what you are saying, but i apply left rudder when i take off with a cross wind from the left :confused: does that actually yaw the plane to maintain heading or does it balance a yaw? :confused:

sorry i'm just doing PPL, my knowledge is shallow

FlyingMoggy2

I not sure if you are for real or not. Maybe you are trying a wind up? Who knows? I will give you the benefit of the doubt for now. To keep it simple, what would you do if the aircraft commenced an uncommanded yaw to the left? You would apply right rudder to stop it and vise versa. What do you think will happen if you applied left rudder? I strongly suggest you get a grip on this principle before you hop in a twin engine aircraft because if you don’t it may kill you one day.

Sorry bout that i got somethings a bit confused ^^
Now its all cleared up, thanks 404 Titan.

I have found the most complete, though concise explanation of dutch roll from this site:

http://142.26.194.131/aerodynamics1/...ity/Page5.html

I found this easier to picture than either Davies' or the Naval Aviators explanations. And of course, dutch roll has nothing to do with stall, though I have spoken to a colleague of mine who used the Bristow explanation in his interview and got a grilling from it!

I have also spent a few hours pulling hair out over Bristow's errors, and have a few more errors to add, but it'll have to wait until after my interview - too busy studying now!

I think something else needs highlighting here that has been missed.

FM2 states

"but i would've through upon reaching glide slope you'll just shut down the remaining engine(s) for a glide approach"

Steady on there Chap ! You'll kill us all. If you have 2 engines (or any number infact), and one fails, are you really going to shut down your last engine(s) ? Think about going around, going low and slow on finals etc and what options you leave yourself if you've shut down all your engines ? I would wager that you'd do everything in your power to keep that engine going !!!

Be careful about what you write on PPruNe Vs what you know/ are confident about stating. ;)

Anyone who's bought the book willing to sell?

Jinkster

Page 132
And also the topic about Given a deviation from ISA of 36C (warmer), the pressure altimeter will; Overread, underread or the same. His answer was overread. It will overread only if the temp is colder than ISA. Maybe he just forgot to put the negative sign or something.

Yes, I believe a grain of salt or three might be in order there;) .

Does anyone agree that the info on pages 60 and 195 regarding crosswind effect on an engine failure is absolute bolleaux?

Assuming a positive weathercock tendency then surely the upwind engine is the critical one and consequently the "best" engine to lose (see question p 195) is the downwind one?

I thought I knew the subject before I started reading some of this rubbish.

edited for spelin!

I agree, I would prefer a loss of the downwind engine, it's effects would be mitigated by the weathercocking tendency.

I think it's another one of those cases that this book is bass- ackwards, but it keeps you on your toes!
S

Page 262 What are Supercooled Water Droplets (SWD's)?

Figure stated in book is that supercooled water droplets can occur down to -45 degrees celcius.

ATPL study books as well as for CAA exams have taught me that SWD's occur up to -40 degrees celcius. Other independent meteorology web sites and in particular, the official "Bergeron Process" states that SWD's occur up to -40 degrees celcius also.

Boeing Operation techniques for use of Anti Ice state that at -40 degrees and below does not require anti ice.

So I think Bristow though correct with the explanation, is incorrect with the temperature figure he states.