CRJ 700/900 Wing A/I XBleed Valve vs ISOL

[Smoked Toilet]

In a CRJ 700/900, the wing anti-ice cross bleed valve is used to connect the left and right anti-ice duct together in the event of an engine failure/wing anti-ice valve failure/bleed valve failure. When selected, it electrically opens the cross bleed valve, and closes one of the wing anti-ice valves.

Pretty straight forward.

However, on the ground, we were able to heat both wings on a single engine. The isolation valve was open, and the air from the right engine went past the isolation valve, straight up the left anti-ice duct to the left wing.

The isolation valve (when in Bleeds Auto mode) :
1) automatically opens when both engine PRSOVs are closed and the APU is supplying bleed air.
2) cycles open and closed during crossbleed starts or right engine start using APU bleed or external air
3)cycles open or closed during the auto transfer of bleeds between the APU and engines.

Does anyone have any knowledge of how these systems work? Is it possible that we could heat both wings, in the air, with one engine failed, and not using the xbleed selector valve?

Thank you

ST

[Mad (Flt) Scientist]

Yes it is possible, since there is a flow path there.

However, it's not how the system was designed for the WAI performance, so you shouldn't rely on the ISOL valve in lieu of the WAI xbleed valve. Because the system was certified to perform with the xbleed valve used, not the ISOL valve. Basically, I doubt anyone will assure full evaporative anti-icing for the OEI case using only the ISOL valve.