Originally Posted by
C195
To expand a bit... I have never flown the the ATR but I met a friend recently who does and we were discussing the type and comparing it to the 340. The white bug/ red bug/ icing/ non-icing stuff seemed a little confusing at first.
For example (if I understood it correctly!), when using non-icing speeds you can select high bank at white bug if you keep the flaps at 15 degrees or you can retract the flaps at white bug and remain at low bank. But, you can't retract the flaps and select high bank at white bug.
Seemed reasonable. But, when using icing speeds you must wait until white bug+10 knots before you can select high bank (keeping the flaps at 15) or you can retract the flaps at white bug +10 knots but then you have to wait until red bug +10 knots until you select high bank. Did I understand it correctly? Anyway, whether I did or did not, it certainly seemed a bit complicated... green bug, yellow bug, white bug, red bug... + normal & icing conditions. The Saab was a bit simpler.
It is probably not that complicated. Just try to separate the icing conditions from non-icing conditions.
I wasn't on it very long but from what I can remember off the top of my head....
On all takeoffs, we set white bug and red bug speed. But depending on the environmental conditions, we ignore one of them for normal operations.
Usually we are in non-icing conditions. In this case, when accelerating through white bug speed, we can now retract the flaps(so it is your min clean speed). Because there were no icing conditions, you ignore the higher speed red bug even though it was set for departure.
But you are restricted to low bank(max 15°) until 10 knots higher at which time you can select high bank for the flight director and fly the aircraft at the higher bank angles. Therefore ATR came up with a complicated acronym calling this speed Vmlb0(
V min for
low
bank for
0° flap). Many jets have some sort of restriction like this. Seem to remember a max 15° bank until V2+10 on the 737-200. 744 has similar to the ATR but only when heavy above 309,000 kg, so it is a common kind of thing, however they don't have a manual pushbutton for high bank/low bank on the flight director like the ATR.
In icing conditions, you can ignore the white bug for the most part and now use the normally ignored red bug for flap retraction speed. It sits about 10 or 15 knots above white bug speed depending on your weight. In this case, as you accelerate past white bug on takeoff, you continue and the at red bug do the same thing with the same type of bank restrictions.
Sort of similar for decelerating. White bug is normally your min clean speed unless in icing in which case it is the red bug. If I remember right, in severe icing, make it red bug+10.
That being said, white bug is your best lift to drag ratio(so therefore used for a driftdown target speed) and if you lose an engine on takeoff whether in icing conditions or not, you target white bug once above the acceleration altitude. But the red bug still applies for flap retraction purposes which may never be reached in some cases. That is why 4th segment can be more limiting than second segment on the ATR in some cases. Because of extended flaps.
There is a Vmhb0(high bank) as well in the ATR which is several knots above Vmlb0. This is retrieved from tables for reduced flap landing procedures.
The yellow bug, a target for a go-around speed. Green bug is V1 if different from VR which was an orange internal bug.
O.K., I went back to my notes. Vmhb0 is 1.3 times VS, Vmlb0 is 1.25 times Vs(maybe ATR did all this so they could certify with lower speeds and therefore better capabilities with some restrictions such as bank angle.) Vmlb for flaps 15 is V2.
But in icing conditions, the ratio is higher between Vs and min bank speeds as a precaution. Vmhb for flaps up or 15 is 1.5 times Vs, while it is 1.45 for Vmlb0. I see 3 different groups for flaps 15 with Vmlb15 ranging from 1.32 to 1.45 depending on what phase you are in(takeoff 2nd segment, normal climb, go-around). This is actually ATR-42 stuff by the way.
In the end, you don't really need to know this last portion, just follow the appropriate chart for takeoff and setting of bugs for approach and go-around and retract your flaps and limit your bank angles as appropriate, which is a limit of 15° until 10 knots above the white or red bug as appropriate for the conditions you are flying in.
Final approach speed is your orange internal bug which is at Vmhb 30 meaning proper protection is provided at 30° bank such as on your circling approach.