Hydralic System Limitations on a Twin Otter

[Rudder]

I was wondering if anyone would know the temperature limitions on the hydraulic oil of a twin otter. I understand that it is -40C but would like to confirm it if possible.

[T&B]

Not sure what the end result you are looking for. The hydraulic fluid used in the Twotter is the standard general aviation red stuff MIL-H-5606. The Shell Oil web page (sorry, too compuker-illiterate to set up a hyperlink)says their version (Shell 4) has a pour point of below -75 F. The Canadian Operators Kenn Borek Air took a pair of Twotters down to the Antarctic mid-April this year, and had no reported problems in -68 C.

[Rudder]

Thanks T&B.

I may have missled you in the way I framed the question. I am after any Hydralic System temperature limitation on the Twotter.

Some aircraft will have for example a -40C limiation on the hyraulic system for operating the flaps or a rear cargo door. This is not a limitation on the ambient temperature or a limitation on the oil but a limitation on the hydraulic system itself and I would think it relates to the internal pressure of the system due to the viscosity of the oil at low temperatures and the chance of say blowing O-rings or seals.