ATR Pilots - use of LO BANK for turns

[Rookie.Pilot]

Dear all,

Thanks for helping, in advance.

I'm relatively inexperienced on the ATR having only about 1000 hrs on type.

I have been flying various Turbo Props before, this being the only one with the LO BANK/ HI BANK feature used for angle of bank; LO BANK being 15 degrees and HI BANK being 27 degrees as all of you know.

I have always believed in passenger comfort as the priority with safety in mind ofcourse striving to acheive smooth flying in all stages of the flight.

Also aircraft performance depending on Weight, Altitude and Temperature limits, would always favour for a LO BANK in most stages of flight.

Ever since starting on the ATR I have always used LO BANK and finds it gives a nice compromise between operational and safety requirements, in most cases satisfying both.

Also I have found using HI BANK makes it very uncomfortable for the passengers at the back especially when operating at the slow or fast end of the speed spectrum.

I have been asked to make a case for the use of LO BANK as opposed to the use of HI BANK. I am keen to get as much feedback as possible from all you Experienced ATR pilots, TRI's /TRE's, test pilots and line pilots as well.

Many thanks again

Rookie:)

[DB6]

Not ATR but Saab 340 - also has 1/2 bank mode. Can be used most of the time but you have to remember to take it out for holds, approach etc as these are based on rate 1 turns. I have never found full bank to be uncomfortable in the back, we normally use 1/2 bank for initial climb/engine failure and if climbing at below approx. 1.4 Vs (I think), then get rid of it as it's a bit of a pain after that.

[STBYRUD]

My 737 banks up to 30° on LNAV - mighty uncomfortable though - I personally try to avoid it if I can. Get it on a proper heading with heading select (we can choose a bank angle in 5° steps, standard turns out to be 25°), then let LNAV rip. Have you gotten any comments from your colleagues on your technique?

[con-pilot]

Not ATR but Saab 340 - also has 1/2 bank mode. Can be used most of the time but you have to remember to take it out for holds, approach etc as these are based on rate 1 turns.

That is how I use the half bank feature on all the aircraft I have flown that have the half bank auto-pilot/FD function. And yes, I used it primarily for passenger comfort.

[Rookie.Pilot]

Yes I have.

I personally try to explain to them in detail, about the things we are talking about.
Very few seem to understand what I'm getting at.
Nevertheless, I'm persistent and try to do my leg as smooth as possible.

Yes, incase the heading to come exceeds more than 60 degrees, leaving LNAV engaged will take it very sharp. I do the very same thing you mentioned, about going on heading select, LO bank , turn onto the fix, zero the deviation then re-engage LNAV. Comes out very smooth.

Comments from the back are rather encouraging too. Had a few pilots tell me that on LO bank they hardly felt her turning.

I'm after the finer points to include incase I'm asked why I am to use LO bank.

As it stands there are 3 very senior captains who alL stand by me on this.

They said, LO bank gives better performance, speed stability in sharper turns, keeps you away from the circuit pattern at major airports especially those with dual runways, the margins of recovering from a stall at such an angle of bank is greatly increased, also pax comfort, to name a few. Not to forget, an engine flameout while in the turn, makes it very hairy when you are in HI bank.. try it in the sim to confirm. So LO bank suffices well for this too.

I am aware that ATR specifies it is possible to use HI bank when you are white bug VMLB 0 + 1 kt.

But to my knowledge no where has it been mentioned that HI bank is mandatory. Even the default selection comes on in LO bank due to the speeds being below white bug for the initial climb.

Just wondering if there are anymore things all you very experienced gents can think of to support my case.

Thanks again guys,

Rookie

[Piltdown Man]

When to use...

Lo Bank - For N-1 when flying V2+10 (or less...urgh!)
Hi Bank - For normal aviation.

There is no need to be cleverer than this.

If a turn is done smoothly, few will realise exactly how much bank has been used. The comfort will not be compromised if a balanced turn is done smoothly.

PM

[BrasiliaCaptain]

Rookie.Pilot,

I haven't flown an ATR in almost three years, but I did fly it for two US operators, and I was also a simulator instructor and line check pilot on it.

A bit of background for non-ATR people. The ATR has quite a few speeds that a pilot must bug or observe. They vary among operators in name, but they all follow a script. ATR assumes most pilots fly with the autopilot/flight director most of the time. They have minimum clean speeds for LO BANK (15 degrees maximum) and HI BANK (27.5 degrees maximum). These speeds change when you are flying the airplane in icing conditions. When you select one of the anti-ice systems on (specifically the horn heat), the stall warning thresholds are changed to a lower angle of attack to compensate for the earlier separation of airflow on an icy wing.

We had discussions about LO BANK/HI BANK quite frequently but most pilots and instructors within our organization did the following:

During terminal operations (departure and arrival), airspeed/icing conditions permitting, we used HI BANK. In fact, departing in icing conditions, we would often increase our airspeed a few knots above profile to get to minimum HI BANK speed so we could turn tightly. We flew in very busy airspace, and being a slower airplane, ATC expected us to turn as tight as possible departing and arriving at the hub. Often, after leaving the terminal area, most guys, including myself, would select LO BANK for passenger comfort.

When following instrument approach procedures, speed, configuration, and atmospheric conditions permitting, it is important to use HI BANK if you will be flying the procedure in heading mode. At my last operator, our ATRs didn't have GPS for navigation. So our pilots would fly VOR and NDB approaches in HDG mode (NAV mode didn't work very well with the VORs in our route structure). Keep in mind, the difference in turn radius between 15 degrees of bank (LO BANK) and 27.5 degrees of bank is close to double, so you can see the importance of using HI BANK conditions permitting in this situation to ensure that procedure turns, holding pattern entries, etc. worked out well.

As far as the safety aspects of using LO BANK versus HI BANK, I'll make the following points. True, stall speed is higher with a loaded wing, i.e., in a turn. Which is precisely the reason ATR provides minimum HI BANK speeds for maneuvering protection in icing and non-icing conditions. So this is accounted for except in the case of severe icing, in which case, 1 g and 0 bank angle might be more than the wing can handle anyway. As far as an engine failure in a turn, I have given and received many of these during turns in HI BANK in the simulator. It's never fun (I guess that depends which seat you're in that day), and it might be more manageable with a lower bank angle, but keep in mind that we are professional pilots. I am pretty sure the outcome of each of your attempts, while hairy, was successful?

So as far as it being mandatory, I am not sure what your airline and regulatory authorities say about it, but my biggest concern about flying almost exclusively in LO BANK would be turn radii when being radar vectored at busy airports and when conducting instrument approach procedures using HDG mode.

[FougaMagister]

In my outfit, we fly all SIDs in LO BANK, since these assume 15 degrees angle of bank turns (as usually noted on the Jepps). As soon as we get radar vectored (such as taken off the SID with direct routings), we switch to HI BANK, since ATC expects rate 1 turns. That is of course, provided we have white bug +10kts in normal conditions, or red bug +10 in icing conditions. As for PAX comfort... we fly cargo.

Remember that even in LO BANK, the AP will in LOC* make turns with up to 30 degrees angle of bank if required to intercept the ILS.

Cheers :cool:

[BrasiliaCaptain]

Fouga,

Very interesting about the SIDs and half bank. Most of my flying experience is in the US.

Oh, and in LOC*, it will actually do up to 33 degrees. :) I miss that autopilot. Maybe I'm showing the limits of my aviation experience, but I've never used a better autopilot since.

[FougaMagister]

I stand corrected. Time to open the FCOM again methinks...

Cheers :cool:

[FCeng84]

Rookie,

I am not a pilot, but have spent my career in design of flight control systems. I am very familiar with flight mechanics. A quick look at a little physics/math might help your cause.

The the heading rate during a turn scales with the tangent of the bank angle. (Turn radius scales with the inverse of the tangent of the bank angle.) The steady normal load factor during a turn scales with the inverse of the cosine of the bank angle. It is interesting to compare the two bank angles available with your autopilot:

Bank_ Tan_ 1/Cosine
15 deg 0.27 1.035
28 deg 0.53 1.133

From these data you can see that increasing bank angle from 15 to 28 degrees does not quite double the turn rate (or not quite halve the turn radius) while it increases the incremental load factor by almost a factor of four! (1.133 - 1) ~= 4 * (1.035 - 1)

Where your flight operations permit a half rate turn the payoff in reduced load factor change for your passengers seems well worth it.

I hope you find this comparison helpful.

[uncle_john]

Maybe, something from my experience.

Every time, when I have possibility traveling as passenger in lusty ATR, I ask about last row. It's part of my private super top secret scientific research. I try to hear how passengers comment what's actually happening on board (especially extra situations connected with traffic, weather, etc.). It helps understand what passengers like, what dislikes, etc...

As We know, good pilot in cockpit it's lazy pilot ;) (it was always said to me by my instructors, and i have to agree with this). In my small company we execute most of departures as RNAV, so as we all now when we hit out NAV button Flight Director will draw our turns with more than 15degrees. During departures passangers are benumed mostly by beauty of ATR engines and propellers. (I've never understood how people can tolerate that noise). I (and probably passengers too) always begin hear my own thinging about 10minutes after take off. I've never remember which BANK (LO or HI) was used by my colleagues in cockpit. So consideration is easy. Passengers aren't able to feel additional amount of comfort (when depart is in LOW BANK) because noise, vibration, and shock created by ATR during depart kill comfort thoroughly.

So in my opinion discusion about LO or HI BANK during departure propably is interesting, but it is exactly as discusion about which hols are more important - Christmas or Easter? Conclusions: Cross FL100 as soon as possible and open your meal... ;)

Little better is during our loooong cruise. Supplicatory prayer of calm is finished (of course calm is still only a dream), and I (when fly as pax) always starto to be interested what's happening and where we are. So during cruise and during initial approach using LO BANK is very good idea, and it's small chance to improve comfort of our guests on board.

Special phase of flight when I ALWAYS use LOW BANK is holding. Also I always ask controler about possibility of extending outbound (sometimes it's 4 minutes !!!). I know, that passengers dislike manouvers in holding pattern (especially when it's full AT7, because then pitch during Hold is almost 5deg when ias is 160=170kts).

See you on TCAS

uncle_john (Poland)

[Rookie.Pilot]

:ok:Really interesting comments from all of you.
Very obliged and thanks again.

I liked the flight mechanics part of the explanation.
It wasn't very clear to me and I'm trying to understand all what you said so it would be easy to explain to them in simple terms.

Thanks again and please do keep the comments coming,

Rookie:)

[FCeng84]

Rookie,

The short summary is that for bank angles of 30 degrees or less, doubling the bank angle of a turn roughly doubles the turn rate (or cuts the turn radius in half) at the expense of increasing the incremental vertical acceleration by a factor of four. If your flight segment does not require the turn performance associated with a 30 degree bank, your passengers will definitely find the ride smoother/calmer if you can limit bank to 15 degrees.

[Rookie.Pilot]

FCENG 84...
Mate thanks again.
Have just demonstrated your art of flight science and got some guys to believe me on the line. Positive results. Better Pax comfort suffices this too.
Good comments from guys who were paxing as well at the back.
Also, in terminal airspace i would guess a jet aircraft of 737NG class would have the same turn radii as an ATR doing the same turn on LO BANK since the jet is subjected to a higher speed in the turn resulting in a wider turn radius even with 30 degress selected on its' MCP. correct?
stand to be corrected..just simple turbo prop guy here