Saturday, May 12, 2012

A "Little 1/8 of a inch" may save the day!

A instrument scan can be a lifesaver. Who would ever think an insignificant instrument, like a anmeter, could capture my attention. What's a "Ammeter" look like? Hit me! Herein lies a tale that may save your life.

Flying a 1964 S Model Beechcraft to and from Cat Key in the Bahamas one day many years in the past I was, as usual, performing a routine instrument panel scan. Something didn't seem right. I scanned again. There was the problem. The normal indication on the anmeter was "off".

Flying the same airplane trains you to be aware of all the sounds, vibrations and readings that are normal for the plane. Today, roughly 100 miles East of Ft. Lauderdale International Airport and Red Aircraft, my anmeter gauge was off by 1/8th of an inch. It was slightly to the left of dead-center. It normally registers 1/8th of an inch into the positive range while the plane is operating.

My first thought was instrument failure or a calibration problem. The plane was operating normally and all instruments were working properly. What was the problem. In the Beechcraft the anmeter indicates the alternator is charging the battery properly. Without proper charging instruments that depend on electricity to function begin to fail.

Just to be safe, I contacted Miami Control and reported a possible electrical failure. The anmeter was not indicating a charge to the battery. Miami Center told me to squawk a frequency to identify my aircraft and position through a "I-Dent". I dialed in the frequency on the transponder and pushed the ID button. Miami confirmed my position and altitude because the the plane was outfitted with an encoding altimeter as well as a transponder.

Once position was established the controller at Miami Center told me to shut down all electrical equipment except for the communication radio I used for Miami Center. He told me to change my aircraft heading slightly to the right to counter a drift away from the route to Ft. Lauderdale.

I did what he instructed me to do. The radio needed electricity for communications and the aircraft engine received a spark from the magnetos that ran independent from a battery source.

After visual contact with Ft. Lauderdale International Miami Center turned me over to ATC and I landed, without incident. I switched over to Ground Control to proceed to Red Aircraft's Service area. Once there, I had the A&E Mechanic check over the anmeter and alternator.

The belt that rotates the alternator was fine and the anmeter functioning. You could see the alternator pulley spinning as well. The mechanic shut down the engine and removed the alternator.

Beechcraft was notified that all three welds that attached the rotating belt pulley to the alternator armature were broken. If the armature wasn't rotating the alternator wasn't producing a charge. Without a charge the battery couldn't provide the electricity for electrically operated equipment.

On a night flight the loss of navigation equipment for safety in flight is very serious. Critical instruments in a plane certified for Instrument Flying have dual backup to provide electrical and vacuum operated equipment for safety. If electrical failure occurs the vacuum operated equipment can take over for control purposes.

Beechcraft issued a FAA Directive to inspect all Alternator welds in Bonanzas to prevent further breakdowns, like mine, from occuring.

"1/8th of an Inch." A lesson in observing what your instruments can tell you.