Ever wonder why the standby alternator or vacuum pump isn’t working? There is a drive coupling that is designed to break if something becomes stuck. They are also supposed to be replaced every 500 hours or they can start looking like this!
Ever wonder why the standby alternator or vacuum pump isn’t working? There is a drive coupling that is designed to break if something becomes stuck. They are also supposed to be replaced every 500 hours or they can start looking like this!
![[Credit: Wikimedia Commons]](https://www.kitplanes.com/wp-content/uploads/2026/07/4_rutan_a_longez.jpg_preview.jpg?w=218&h=150&crop=1 "Rutan Symposium Turns to the Coming Canard Maintenance Crisis")
![[Credit: Lisa Turner]](https://www.kitplanes.com/wp-content/uploads/2026/02/Fuel-Selector.jpg?w=218&h=150&crop=1 "Fuel Follies")
last time I looked, the vacuum pump drive spool had a 500hr OR 10 year service life whichever comes first.
Perhaps this is newer data than when you last looked, butTempest has a service letter, SL-001 which recommends replacement every 6 years.
In our glass cockpits the standby alternaotr seems pretty important. That’s why we recommend 5 years.
Vic
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