Bank Angle + Cabin Altitude

[st1322]

Hi,

Two questions regarding use of bank angle limiter and cabin altitude. Before I have only flown 738 by PMDG and there was automation on both systems. Classic is a bit different

1. Bank Angle - how to use it properly? Take off - 30 degrees, but should this be limited in cruise flight?

2. Cabin Alt. I know that I have to set FL and landing altitude and change the system to flight from ground. But there is also possibility to set the desired cabin alt. How is this used/operated. Should it be at zero all the time?

Tom

[mfor]

The pressurization system has 2 (semi) automatic modes of operation:

1) Automatic - you set the FL and the destination altitude and the system will capture the take-off altitude and return to that level on a aborted climb and target the destination altitude for a normal descend.

2) Standby - you set the desired cabin altitude and can also make manual adjustments - this is useful for non standard flights, e.g. touch and go training.

There are also two manual modes (AC and DC powered) where you control the opening of the outflow valve manually - this is for emergencies only (e.g. when ditching you'd close the valve manually to prevent flooding and turn off the bleeds to still allow de-pressurization)

The flight/ground switch will activate/deactivate the system, however it will also automatically engage when there's no load on the wheels.

For normal flights you would use automatic entering FL and destination altitude. I think it's also part of the procedure (may depend on operator) to set the cabin altitude to 200 below field elevation, so in case you quickly need to switch to Standby the plane will be fully de-pressurized when landed (the auto system handles that automatically afaik).

 

As for the bank angle I think I remember someone (Litjan?) saying it should be lower at high speeds, however IIRC LNAV will disregard any limitations to follow the route.

Edited January 21, 2018 by mfor

[st1322]

Thanks.

Regarding bank angle. I noticed that the turns in LNAV in cruise are very sharp, too sharp in my opinion.

[Shanwick]

There is a logic in the real plane that limits bank angle at higher altitudes. Would be great if this gets implemented in the IXEG one day.

Edited January 21, 2018 by Shanwick

[Litjan]

Mfor has the answer for the pressurization system. The only thing to add would be that the AC manual mode is very fast (to quickly open/close the valve all the way) and the DC mode is slow (which makes manual pressure rate control easier).

I also see a lot of videos where they set the landing altitude in automatic mode to field elevation -200´. This is not necessary, the automatic mode will control to entered altitude -200´automatically. When using standby mode you want to set the cabin altitude according to the max pressure schedule (the little black placard right underneath the panel). For landing set it to field elevation -200´.

For LNAV turns:

The logic in the real plane plans the turns at high speeds with a radius that demands less bank (cruise flight). The bank limit per se is still 30 degrees for LNAV - so if there was a sudden crosswind threatening to push you off this shallow turn, the bank would increase to stay on the magenta.

We don´t model this "cruise planning" yet, thats why you see the (too steep) turns.

Cheers, Jan

 

[st1322]

Thanks Jan. So, one way of “fixing” what is not implemented could be manual limit of bank angle? If yes, to which setting?

Tom

[Litjan]

Hi Tom,

just like in the real plane, the bank angle limit selector only has an effect in HDG mode. In VOR/LOC and LNAV bank is always limited to 30 degrees, regardless of the bank angle limiter.

The only way to avoid high bank angle during cruise would be to fly the turns in HDG mode (with the limiter set to 10 deg, maybe), or in manual flight. This sounds a bit like too much trouble, but I flew with a Captain once that made it a habit to always "cut the corner" a bit in HDG mode, fantasizing about how much fuel and time he saves for our company.... One of the toughest skills to master as a First Officer is when to just keep your mouth shut and nod and say "wow, that is a great idea, Captain" - and when to say "I have control! Go-around!"

Jan