Queries: 06/02

Excess Precession?
Ive been flying a Mooney M-20J for 10 years and have noticed that the vacuum-driven heading indicator seems to precess at different rates at different times.

Sometimes, Ill reset every 10 minutes or so, other times more like every 20 minutes. The airplane was new 10 years ago when I bought it, by the way, and the vacuum system is fine.

The vacuum doesnt vary according to the gauge and my mechanics say theres nothing wrong with the instrument. Whats your view?

-Paul D. Larsen
Fargo, North Dakota

You didnt mention if the heading indicator is an HSI. If it is and its the slaved Century NSD-360 commonly found in Mooneys, we would suspect problems in the slaving mechanism or wiring.

If its unslaved, our guess is that the instrument is slowly declaring itself in need of overhaul, assuming the vacuum pressure is up to snuff. If it has gone 10 years with no service, its about due.

The same is true if the instrument is a plain-vanilla vacuum driven DG. Again, assuming the vacuum is okay, excess precession is often a sign of bearing wear and an overhaul may be the only option.


Over Gross Sham?
I read with interest your article about turbine airplanes gross weight problems followed by the comments from William Lear Jr. on the same subject.

I have long felt that gross weight and CG are among the most ignored limitations in all of general aviation and am willing to bet that many of the pilots of these turbine airplanes pay little attention to gross weight.

I have been a pilot for 25 years and an Army Aviator for the past 19 years. Due to my respect for gross weight, I have always owned airplanes like the Cessna 180, Piper Comanche 250 and 260 and, for the past five years, an Aztec.

Over the years, I have watched many people load their airplanes 10 to 20 percent over gross with no apparent ill effect. Am I being ridiculously over cautious?Are these gross weights just way oversafe numbers designed to protect the manufacturer?Is exceeding the gross weight just part of the risk assessment process that we all do prior to flight?

-Howard Swan
Fort Campbell, Kentucky

As law abiding aircraft owners, its our duty to inform you that you should always adhere to the FARs when flying. Having dispensed with the boilerplate, youre right: the reality is that many pilots do fly over gross from time to time.

The gross weight limit on an airplane isnt a CYA safety margin but a hard value determined by and demonstrated during certification. FARs aside, we think busting gross weight limits should be avoided whenever possible. (Yes, we know thats difficult to do at times. Then again, you rarely have to fly anywhere.)

In both singles in twins, over gross saps takeoff and climb performance and in twins, it greatly increases a bad outcome following an engine failure. If you venture into the world of over gross operations, stack the deck in your favor by avoiding it on high density altitude days or from short or obstructed runways.