Ammeters Pro and Con, & Flying like there is no tomorrow.


I got a very well thought out letter our friend Dave Aldrich in favor of Ammeters. In a previous post, I had said I did not like them in aircraft. Dave writes in to give another perspective. He explains his case well. I want builders to learn and make an educated choice. Dave’s position is educational, even if you don’t go with an ammeter, you will better understand what it is supposed to do if you read his letter.

I have two main objections to ammeters: They often bring fat, high current lines into the cockpit, in close proximity to things like header tanks. In most installations I have seen, these are not protected circuits. The Wagabond had ammeter in the panel, and it had 4′ of #10 wire running to it and back to the bus. This was hot and unprotected any time the master was on. By deleting this, every wire now in the cabin is 16 gauge or smaller and they are all covered by fuses. Second, most ammeters hardly ever show more than one needle width deflection in full operation. I don’t think that it is very likely to catch a pilots eye if the system is discharging slightly. A tiny low voltage light will do a better job of this.

The most important point in this article is one that both Dave and I agree on, and I cover it in the comments below Dave’s letter.

“Hi William, I’m going to suggest that you rethink your position on ammeters. A correctly installed and properly interpreted ammeter will provide as much useful information as a voltmeter. To disparage them with an offhand remark is unwarranted and unjustified.

There are basically two things that any electrical monitoring system (voltmeter or ammeter) must detect. The really important one is alternator failure, and the other is abnormal loads caused by equipment malfunction. Let’s look at the options. Ammeters that read alternator output (like my Piper Cherokee) provide positive indications of alternator failure and of unusual loads. If the current reads zero, the alternator is inop. If the current reads abnormally high, then it’s time to see what’s causing the extra load before the smoke leaks out of the wiring.

The ammeter in the battery line also provides a quantitative idea of current use once things are started and stable. Negative reading (current going from battery to loads) – bad. Large positive reading also not good. Small positive — eat your sandwich. It can also be useful in load control during an alternator out/battery only flight. The only down side to ammeters in general goes back to 2 words in the first paragraph — “correctly installed”. The addition of an ammeter shunt and the simple wiring associated with it is not without potential for stupidity but it’s a lot less risky than many of the other things people strap onto the fuselage.

Voltmeters also provide the necessary information on alternator health but there can be some ambiguities. If there’s an unusual load, the first sign will be either smoke or the alternator C/B popping. If the voltmeter reads 13.9 — above basic battery but below normal regulated voltage, what’s wrong? Is the alternator starting to die or is the battery dying? This is the time when the Piper type ammeter will tell the tale. The +/- ammeter and voltmeter will not. I do grant that in most of these situations, landing is THE prudent option and any of the system monitoring devices will lead you down that path if you’re paying attention. The single real advantage I see with voltmeters is simplicity of installation. Two wires that have lots of places to be attached can’t be beat.

One useful data point provided by McDonnell-Douglas. The DC-9/MD-80 has a rotary switch that monitors a bunch of functions in the DC electrical system. Would you like to guess what the normal in-flight position of the switch is? Battery charging amps. Yes, I know it’s not apples to apples but still…Having said all that, I agree with you that if I must have just one electrical system monitoring device, the voltmeter is preferred but ONLY because of it’s simplicity. KISS wins. Respectfully, Dave Aldrich”

Four pilots that personally taught me a lot were four men that spent many years each,  flying like there was no tomorrow. Their names were Nat Mathison, Charlie Traghber, John McGrath and David Cummock. They all flew for the same outfit, and that organization actually incentivized and rewarded pilots for flying like it was their last day on Earth. Respectively, they flew B-36 Peacemaker, B-47 Stratojet, B-52 Stratofortress and the B-58 Hustler. Their outfit was the Strategic Air Command.

Each of these men personally told me that they fully understood that their only task was to get their nuclear weapons to the target. They were not there to preserve their aircraft; it was expendable, if damaged, they were continuing to the target, they would not abort nor divert. Their lives were of no consideration; if it slightly increased the odds of getting to the target, but doomed the crew, so be it. The first three said that they only given vague and unrealistic post-strike flight plans, like flying to Turkey or Iran. They all said that they would choose to expend the fuel to increase their final attack speed and forfeit the possibility of escape.

McGrath was my aerodynamics professor. He once explained a B-52 wing 15 second MITO (minimum interval take off) pointing out that an aircraft that weighed 490,000 pounds that lost two of eight engines would not fly, but the crew was trained to run off the end of the runway at full remaining power without any attempt to brake, a certain death that would give the aircraft behind you the best chance of clearing your vertical fin and going on to their target. A young student in the front row of the class said with disbelief “No one would do that.” Livid at what he perceived to be a grievous insult and a complete slur against SAC, McGrath put his shaking face right up to the kid’s and said “Every Airman in my wing would have done it.” Charlie Trauber explained that their families lived on the SAC base, a certian Russian ICBM target. For these crews planning a one way strike was easy; they would have nothing to live for.

Had these men been ordered past their Fail-Safe points, there literally would have been no tomorrow. Their flying had a purpose, their proficiency and commitment was a deterrent to war. Yet I have met many people who also fly as if there is no tomorrow, but their flying is different in two ways; they fly light aircraft and their flying has no purpose.

In Daves discussion he states “I do grant that in most of these situations, landing is THE prudent option and any of the system monitoring devices will lead you down that path if you’re paying attention.” This is a vital lesson in flying that many people miss. If you are flying a plane and all the systems are not working, the only intelligent choice is to land the aircraft at the nearest airport and solve the problem on the ground. This may sound like common sense, but foolish pilots often will fly on with some partially working system. This is called “Get-there-itus”, and it kills a lot of people each year.

In terms of instrumentation, I frequently read builders justifying certain types of instrumentation or controls to allow them to fly on with some systems not working. We use a DPDT switch to control the fuel pumps and ignitions on Zenith 601/650s. Yet some people will wire their plane with 4 SPST or 2 DPST switches. They are doing this so they can fly on the Electronic ignition and the back up fuel pump if the primary pump is out. (normally the DPDT gives only the choice of Electronic ignition and pump A or points and pump B. It is a vastly safer system from a human factors position.) Let me come out and say that anyone who knowing flies with something like one fuel pump or one ignition inoperative is making a very stupid judgement error, and yet people do this because “I just had to get home.”  They are flying like SAC: as if getting to the target was the only goal, and the plane and crew are expendable.

When builders talk about instrumentation, some times they will reveal that they want enough instrumentation to give some indication of exact nature of the problem, not just that they have some type of issue. I will flatly say that diagnosing problems is done on the ground, after landing at the nearest airport. It isn’t something done aloft, and under no circumstances should any type of partial failure, or failure of back up system justify continued flight. In the world of Corvairs I know a pilot who flew home 150 miles on one ignition, after he got home found that he had pinched one wire under the cap. His rationale? Had to be at work in the AM. We had another pilot break a crank in a 4 bearing engine with a long prop extension. He was right over a grass strip. Yet he tried to fly 14 miles to the next airport because they would have rental cars. He made it 11 of 14 miles, totaled the aircraft. We had a second owner fly a plane he had just bought at full power into darkness because he got a late start on the flight home, but “just had to get there.” I have more examples, but you get the point. People who fly like there will be no tomorrow long enough eventually prove themselves right.

It is hard for me to convey to new people how serious I am about this topic. If you are new, and any one you meet, especially if the person is your instructor, ever brags about fly a certified aircraft on one mag, changes the days flight plan because they are running late, or loweres their standards about weather because they want to sleep at home rather than in a motel, stear clear of this person. I am polite to people who have told me of things like intentionally flying on one mag, but I would never get in a plane with a person who had previously done this. Neither should you. Lowering your standards to those of other people is a slippery slope, it leads only down, and if you do it long enough, one day, without knowing it, you will be flying with no tomorrow.-ww


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