Don’t Get Belted By Your Accessories, Part 2

Just as having belts that are too tight can cause damage to your engine or the driven components, belts that are too loose can also cause problems. These problems can be hard to diagnose, and because they come from the component that is driven by the belt, they may escape detection if you don’t know what to look for.

THE SET UP: While flying a night approach, you flip on your landing light…


  • Your cockpit lights dim as the landing light springs to life. Caution: Don’t convince yourself that the landing light is as bright as it usually is and the real problem is that your windows should have been cleaned weeks ago.
  • Your Comm has become scratchy. You picked up the ATIS at 12 miles OK and continue in for landing, but now that you’re contacting the tower, inbound at seven miles, the Comm is hard to read and even harder to understand.
  • The tower is open, but nobody responds. Your calls go unanswered
  • You see green and white lights flashing from the tower — and it’s *not* the beacon.
  • Your ammeter shows the battery in maximum discharge and, as you glance down to your instruments, the cockpit lights are dimmer than ever.

THE QUICK FIX: You switch off the landing light and your strobe, and the alternator starts to restore life to the battery in time to allow you to extend the flaps and get in touch with a very excited Control Tower. Caution: This will *not* work every time.

You have just been BELTED by a loose alternator or generator belt.

The friction between the belt and the drive pulleys was enough to keep it spinning as long as the load was minimal. Once you switched on your landing light, the huge inductive draw caused more resistance from the alternator and the pulley ‘stalled’ (it stopped spinning.) Without the proper tension, the belt just spun away, and with that, your battery life spun away as well!

Danger: While too much tension is bad, too little can be even worse. In this case, the belt tension was so low that it spun on the pulley. If the tension was just a little higher, the belt could have spun on the pulley and heated up. Under those conditions, the best case would see the belt quickly fail and with it, the driven component … the worst case ends with fire.

BOTTOM LINE Get familiar with the belts in your aircraft. Take a good look at how they look and how they feel when they’re working. That way, if they ever get out of tension, or cracked, weather checked, or lose some chunks, you’ll catch them before they catch you. Remember: In most planes, the only thing between you and the loss of your alternator or generator is one simple belt.