Alternator Check on Run-up...

[avbug]

Generators or alternators shouldn't be applied until the engine is onspeed and stable. When your engine is idling, then engage the generator or starter by turning on the switch. Yo can avoid voltage spikes and transients that way.

 

[midlifeflyer]

Thanks, avbug. So the procedure does have value in addition to "test" value. Nice to know.

 

[avbug]

I'm very big on doing things one at a time. Start engine. Stabilize. Turn on generator. Monitor voltage, amperage, look for decrease in load and battery regains charge. Then as each item is turned on, look for the specific load increase, verifying both that the generator is taking the load, and that the item actually turned on. Check the specific function of the item; turning on a hydraulic pump, for example, should show a load increase, and should show an increase in hydraulic pressure.

In multi engine airplanes, people tend to do dual checks; check mags on both engines at the same time, check both props for feathering at the same time, etc. This isn't a good practice. Check one item at a time, devote attention to just that one item, and move on.

The big thing is verifying the result of moving any control, switch, lever, etc. There should always be something corresponding to what is being done. A few days ago we were using the ailerons in flight, per normal, but found that they felt heavier, and weren't producing the same result. This alerted us to an ice buildup we couldn't see, and in turn a need to leave the cloud. An annunciator failed...we were left with looking for the appropriate reaction, or in this case, an action that didn't match what we expected to see.

Last spring I used a newly installed dual electric hydraulic pump installation to drop a load on a fire, and quickly turned my attention to maneuvering to avoid terrain and climb back out. I failed to check for the corresponding drop in load on the hydraulic pump; I saw the pressure come up, which was what I was accustomed to seeing on that aircraft, indicating that the pump was working. However, it had been an engine driven hydraulic pump, and had recently been converted to the dual electric assembly. This was my first flight after the conversion.

I did an overhead approach, and as I was on short final, the cockpit began filling with smoke. It was filled with smoke about the time I got the tailwheel on the ground, and I was tryin to ventillate and shut off electrical equipment as I was clearing the runway. I made a turn away from other aircraft on the ramp and as I did the hydraulics failed and the airplane entered a slow lazy groundloop. The pump itself was on fire, accounting for the smoke, and it also accounted for the lack of hydraulics...brakes are the only form of steering in that aircraft.

I had seen the pressure come up as I dropped the load, showing that the pump was working, and put it out of my mind. The drop system is hydraulic, and required hydraulic pressure to operate. In this case, with the new installation, it turned on the pump with a pressure switch, and it should have shut off as soon as the tank doors cycled shut. It didn't. Apparently a relay failed closed, supplying continuous power to the pump. If I'd checked the ammeter to ensure the pump shut off, I'd have seen that. Instead, it ran continuously, ran past it's duty limits, overheated, began melting the terminal connections, and caught fire. (the relay also eventually melted).

I throw that out there as an example of why it's important to always check for the reaction as well as the initial action, from beginning to end. In the case of the example multiple responses needed to be monitored; the pressure drop to show the gate system was working and dropping the chemical, followed by a change in the aircraft feel, sound, and control, and then another pressure drop as the doors closed, along with an ammeter increase showing a load as the hydraulic pump boosted up the pressure. Equally important was what I failed to do....ensure that the load went away, showing the pump had cycled off. If I had caught that, I could have pulled the circuit breaker or shut it off manually.

Always verify the response.

As far as components, I like to have everything off when starting, and turn things on one at a time. This is especially true of avionics, but may also protect other system components. If the alternator or generator is turned on before it's up to speed, it's unable to properly regulate as it's coming up, and may result in various voltage spikes that could damage equipment if it's not turned off. Aircraft radios, radar, and other avionics are especially susceptible. Other more seemingly-hardy equipment may also be affected, however, and ensuring that the generator or alternator isn't activated until it's stable and onspeed is a good policy.

Another good reason to have your alternator off during the engine start is that it makes the start easier. The alternator or generator will be trying to take a load if it's on during the start, and this makes the job of the starter harder, because the generator puts a load on the engine as well; it's resistance you don't need when you're trying to do a battery start. Leave it off until everything is online and onspeed, then turn each generator on one at a time and monitor it's effects on the system.