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")
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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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