Atr72

[baobab72]

Hi folks
Even though these questione have been asked in the past, i was not able to locate the proper answers.
In the atr72 and bear in mind that i do not fly turboprops even though i am a huge fan of the atr, why do you have to increase the prop from 77 to 86%Np when you use the anti-ice system - if i am nt mistaken the props are left in the AUTO detent corresponding to 77%Np setting throughout the flight?
does it have to with the performance of the airplane or is it related to the load on the pneumatic system or else?
With reference to the atr crash a few years back in the chicago area due to icing accretion behind the boots, how did that result in a hinge moment reversal? My guess is that the ridge would have caused the detachment of the boundary layer across the top surface of the wing, causing the aileron to flutter and not in a full hinge reversal, but i guess the facts prove my theory wrong!
Finally why is it now recommended to hold in a clean configuration?
Kind regards
Baobab

[Sunstrand]

Hi Baobab,

I cant answer anything about the ATR, but the reason for holding clean is when you have flaps extended you need to have a nose down attitude to fly straight and level, this in turn means you are exposing the top surface of the wing directly into the relative airflow. When you are in icing conditions the ice will build up aft of the deice boot and lead to a stall, In this case the stick shaker will not activate prior to the stall

[JammedStab]

Originally Posted by baobab72

Hi folks
Even though these questione have been asked in the past, i was not able to locate the proper answers.
In the atr72 and bear in mind that i do not fly turboprops even though i am a huge fan of the atr, why do you have to increase the prop from 77 to 86%Np when you use the anti-ice system - if i am nt mistaken the props are left in the AUTO detent corresponding to 77%Np setting throughout the flight?
does it have to with the performance of the airplane or is it related to the load on the pneumatic system or else?
With reference to the atr crash a few years back in the chicago area due to icing accretion behind the boots, how did that result in a hinge moment reversal? My guess is that the ridge would have caused the detachment of the boundary layer across the top surface of the wing, causing the aileron to flutter and not in a full hinge reversal, but i guess the facts prove my theory wrong!
Finally why is it now recommended to hold in a clean configuration?
Kind regards
Baobab

A minimum of 86% NP is used in icing conditions because the increased rotational speed will prevent the formation of and/or improve the shedding of ice and will subsequently prevent the formation of ice aft of the deice boots in the area of the propeller slipstream. In icing incident investigations, ATR identified significant drag increases, and, in some cases, found significant decreases in lift coefficient. ATR attributed the drag increases primarily to propeller ice accretions that resulted from the propellers being operated at speeds of 77 percent, rather than the required 86 percent. According to ATR, "centrifugal effect is predominant to physically eliminate ice on the blades". "Sticking to NP 77% may lead to blade contamination resulting in drastic thrust reduction and drag increase, which could, in extreme cases, push the aircraft down to stall in level flight."


The aileron reversal happened because of the ice accumulation aft of the de-ice boots. Well aft of the boots....in front of the ailerons themselves resulting in airflow disturbance that affected the ailerons which were being held in position only until the autopilot disconnected. Testing has shown showed that ice ridge location is due primarily to the extension of flaps. When in a flaps 15 configuration at a speed close to VFE, the result is a negative outer wing local AOA.

Aileron reversal can happen without ice accumulation but only at very high angles of attack in the stall region. To ensure that this does not happen at lower angles of attack in the ATR, vortex generators have been installed in front of the ailerons to delay reversal. This initially was done on the 72 for certification and as an improvement on the 42. The "Hot and High" ATR-72-210 required an increase in maximum AOA capability. ATR subsequently added more vortex generators of a different design (co-rotative) in front of the ailerons.

The FAA has stated that "…flight testing and analysis have demonstrated that installation of vortex generators on the upper surface of the Model ATR 42 wing significantly improves the effectiveness of the ailerons, which reduces the severity of the roll upset that can occur with asymmetric ice accumulations resulting from icing conditions such as freezing
rain….". Below is a link to an old AD(AD 92-19-01) stating that the installation of VG's in front of the ailerons of the ATR42 cancels an earlier AD requiring manual flying in icing conditions, no doubt due to earlier icing related incidents.

Airworthiness Directives

Under normal ops, holding in a clean configuration while in icing is mandatory. If you are at flaps 15, the aircraft is in a more nose-down attitude allowing ice accumulation aft of the de-ice boots. However, with one engine inoperative, guess what, holding at flaps 15 in icing conditions is approved. After all, you may be below Red Bug speed. Why is this allowed? Because with one engine inop at flaps 15, you are not in as much of a nose down attitude resulting in a positive angle of attack for the outer wings so ice accumulation aft of the boots is less likely. Good thing because Red Bug can be difficult speed to achieve with one engine inop, heavy, higher elevation and in icing.

Old picture prior to VG installation....
Photos: ATR ATR-42-300 Aircraft Pictures | Airliners.net

New ATR with VG installation....There appears to be various styles with some having a large VG.
Photos: ATR ATR-42-500 Aircraft Pictures | Airliners.net

Photos: ATR ATR-42-300F Aircraft Pictures | Airliners.net

Photos: ATR ATR-42-500 Aircraft Pictures | Airliners.net

[baobab72]

Atr

Jammedstab and everyone else thanks for the very detailed and comprehensive reply! Now it all makes sense.
I was reading on the web that when you takeoff with the atr72 you select on the FCP panel HDG and V2+5, if you fly an SID can you arm the NAV mode and then the fd will swicth to NAV at a preset altitude - something like 400ft agl , or you have to manually select it? And the V2+5 IAS command is it armed or it is actually activated? If so does it provides with your pitch setting during normal ops or do you rotate through the command bars to let s say 15 degrees and then you sink the fd, while if you loose an engine you just rotate in the commanded pitch setting? Then at the acceleration altitude you increase you speed to i guess 160 or 180 if you are in icing conditions and as you pass through the bugged vfto you raise the flaps and adjust the pitch to maintain your target airspeed.
Finally, the power management, do you takeoff with the power levers in auto and then you simply select TO on the PWR MNG or do you phisically advance tch the PLs to match the torque computed by the system? Any derated takeoff? What about the prop? Which settings do you use?
Many thanks and sorry if i am abusing your patience but i do love the ATR and i want to learn as much as i can about it!!
Diego

[JammedStab]

I'm afraid someone else will have to answer your questions. FCP is perhaps a more advanced ATR component on the newer models and I don't fly the machine anymore. But 15 degrees seems a bit much of a rotation target for a prop, especially the lengthened ATR-72. Tailstrike avoidance is a big consideration on that aircraft.

But I do have a question for the ATR experts out there on the icing issue. I seem to remember that extended de-ice boots were made mandatory in North America after the Roselawn accident but the Europeans did not because they felt that the accident was pilot error. Have extended de-ice boots been introduced since that time.

[Stuck_in_an_ATR]

I haven't flown the beast for almost 2 years now, but will try to answer some questions...

I was reading on the web that when you takeoff with the atr72 you select on the FCP panel HDG and V2+5, if you fly an SID can you arm the NAV mode and then the fd will swicth to NAV at a preset altitude - something like 400ft agl , or you have to manually select it?

LNAV is manually selected. Can be armed on the ground and becomes active somewhere during T/O roll, but officially should be selected above 400'

And the V2+5 IAS command is it armed or it is actually activated? If so does it provides with your pitch setting during normal ops or do you rotate through the command bars to let s say 15 degrees and then you sink the fd, while if you loose an engine you just rotate in the commanded pitch setting?

IAS V2+5 is active, not armed. However, IIRC, the technique is to rotate to ~8deg pitch and only after liftoff follow FD. That works both for 2 and 1 engine T/O

Then at the acceleration altitude you increase you speed to i guess 160 or 180 if you are in icing conditions and as you pass through the bugged vfto you raise the flaps and adjust the pitch to maintain your target airspeed.

At acceleration you set speed target on ADU - 170 or Red Bug+10, whicever is higher. Then you just follow FD and retract flaps after passing White Bug (in normal conditions), or Red Bug (in icing cond.)

Finally, the power management, do you takeoff with the power levers in auto and then you simply select TO on the PWR MNG or do you phisically advance tch the PLs to match the torque computed by the system?

On takeoff, PL's are advanced to the "notch" position, which gives max rated power for given rating. They normally stay there until Top od Descent and power changes are done via the PWR MGT selector. AFAIK on the older '42 power had to be adjusted manually, but I have never flown the thing...

Any derated takeoff?

Normal takeoff is done with 90% of power. In case of engine failure, ATPCS bumps up the other engine to 100%

What about the prop? Which settings do you use?

Takeoff - 100% (1200rpm)
Climb - 86%
Cruise - 77% (86% in icing cond)
Approach - 86% (77% can also be used)
Go-Around - 100%

On the -500 with 6-bladed props
Takeoff, G/A - 100%
All other cases 82%

On the older versions props are adjusted manually, by moving the condition levers. For Go-Around the CL's are pushed forward by pneumatic actuators.

On PEC-equipped A/C, CL's stay in Auto detent all the time and prop rpm change automatically when moving the PWR MGT selector...

Never thought I'd say that, but I'm starting to miss the good 'ole ATR...

[JammedStab]

Originally Posted by baobab72

And the V2+5 IAS command is it armed or it is actually activated? If so does it provides with your pitch setting during normal ops or do you rotate through the command bars to let s say 15 degrees and then you sink the fd, while if you loose an engine you just rotate in the commanded pitch setting?

According to ATR for the ATR-72-200:

"TAKE-OFF
- As power is increased, the vertical guidance FD bar will move up and lateral guidance FD bar remains centered as runway heading is maintained.
- Rotation is initiated to the recommended value (θ ≈ 9°) as indicated by FD vertical guidance bar."

So would seem that the FD is active during the takeoff roll.

[Vik_atpl]

I fly the 600 with the speed auto , so say you set hdg sel and ias & speed auto on the ground , the fd pitch changes as you go along from rotation > v2+5 >acceleration> climb > cruise , only works on two engines spinning.