ASTO 390 can help to improve auxiliary power unit (APU) starting reliability, particularly coldsoak starting. It is a 3-cSt synthetic diester oil incorporating a carefully selected and balanced combination of additives to improve thermal and oxidation stability and to increase the loadcarrying capacity of the base oil.
Reliable Cold-Soak Starting
Products such as ASTO 390 are commonly used in the APUs of four-engine intercontinental aircraft, but are now being considered for use in twin-engine aircraft.
If a main engine fails, you need to have confidence that your APU will start reliably. An aircraft’s extended range twin operations (ETOPS) certification^ is partly based on the reliability of back-up systems such as the APU. In the event of engine failure, the APU must make up for any reduction in electrical power.
APUs are typically shut down when cruising. During this time, the oil can be cooled to less than –40°C. At this temperature, the viscosity of standard 5-cSt oil increases to about 10,000 cSt. This causes a large viscous drag that may result in a hung start.
ASTO 390, with its much smaller viscosity increase of typically 2,000 cSt at –40°C, can help to improve cold-soak start-up reliability and thus maximise ETOPS times, as it has significantly lower viscosity at cold-soak start-up temperatures (–40°C) than a standard 5-cSt oil.
^ The time a fully loaded twin-engined aircraft requires for single-engine flight to the nearest suitable airport.
Specifications And Approvals
ASTO 390 is fully approved to
Def Stan 91-94 (British)
IPM-10, VNII NP 50-1 4f and 4u, and 36Ku-A (Russian analogue)
Joint Service Designation OX-7.
ASTO 390 is approved for use in all models of the following engines:
Honeywell GTCP 30, 36, 70, 85, 331 and 660 APUs, starters and turbocompressors
Turbomeca Astazou, Artouste, Bastan VII, Marboré 6, Makila and Turmo
Rolls-Royce Conway, Spey, Tay and M45H
Pratt & Whitney Canada PW901A APU
Hamilton Sundstrand APS 500, 1000, 2000 and 3000.