Electrical load shedding

K

kismet

New Member
I was looking through some emergency checklists for a twin that I'll be starting my multi-engine in next month and on the alternator failure check, as with some other electrical failures, there is an item to minimize electrical load. I was just wondering what all you guys would turn off if you were in IMC in a twin.

I figure I could turn off the lights, both exterior and interior (and use a flashlight if flying at night), and one of the nav/comms. Is there anything else you can really do to shed the electrical load? Would you put any flaps down for the approach? Would you squawk 7600 or turn the transponder off? What about if the HSI is electric?

I just thought I would get some other people's input as to what they would do in the case of an alternator failure in IMC.
 
Heya,


Personally I'd turn off the transponder. The radar can still see you whether you have it turned on or not. I would call them up and tell them I had an electrical failure and I only have one nav/com turned on at the moment. I'd leave the flaps up. I'd want to get on the ground FAST and having flaps down does not facilitate that. You worked on your no flap landings, right?

I'm not sure how electric gyro's are tied into everything as I've never worked with them before. I'd assume it's running as long as the master is on? If you asking if I'd pull the breaker for it, I'd say no. It's an important piece of navigation equipment and if you are in IMC you would want to know where you are.

Cheers


John Herreshoff
 
Sorry, I wasn't very clear about the HSI thing. What I meant was since the HSI is electric, it would be even more critical to save battery power any way you could, so would you turn more items off if this was the case? If so, what?
 
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The radar can still see you whether you have it turned on or not.

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Maybe, maybe not. You'd only be a primary target, if that.


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I'd leave the flaps up. I'd want to get on the ground FAST and having flaps down does not facilitate that.

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Whats the hurry? I agree about leaving the flaps up if they're electrically powered, but an electrical failure isn't a dire emergency.


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It's an important piece of navigation equipment and if you are in IMC you would want to know where you are.


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You're forgetting the compass. We practice compass/timed turns for a reason.

Basically, turn off everything thats non-essential and then prioritize whats left. If you have a handheld, use that. Otherwise, let ATC know the situation, get vectors to the nearest VFR or instrument approach and shut off the radios (or at least stop transmitting if the navs and coms are combined)- they use up quite a bit of juice, and everything else thats not absolutely essential. Keeping in mind that you'll probably have to pump the gear down.

Now, all of that being said, since you're flying a twin, you'll most likely have 2 alternators and this won't be much of an issue.
 
[ QUOTE ]
The radar can still see you whether you have it turned on or not.

[/ QUOTE ]

I don't think ATC radar has altitude information, that is one of the reasons for having a transponder.

Correct me if I'm wrong.
 
Here are the major battery loads in amp hours according to Kershner's instrument book:

Beacon light .... 6.0
Position lights . 2.5
Strobes ......... 3.0
Nav / Comm ...... 1.0 recieving / 2.25 transmitting
Transponder ..... 2.0
Autopilot ....... 2.5
DME ............. 1.2
Pitot heat ...... 2.9
Flap Motor ...... 8.5
Lndg/taxi lgts .. 9.0 EACH

These are just the major loads, there are many more loads on the system, but they are smaller such as:

Glide Slope ..... 0.5
Marker Beacon ... 0.1
Interphone ...... negligable

So the important thing is to turn off ALL the lights and pitot heat if not in clouds or icing (use flightlights if at night), turn off all NAV/COMM equipment except for one recieving COMM and one NAV. Save as much as possible for the approach and landing, when you will need power for transmitting. I personally would leave the transponder on at least during the approach so I can be radar vectored to the approach course. Also, know the amp hour rating on the battery. You can realistically expect to have no more than half that. i.e. amp hour rating is 34 amps, you can expect 17, meaning you can run the landing and taxi lights for an hour before running out of juice assuming the battery is in decent condition and you catch the failure right away.
 
I had an alternator failure in a Seminole once. We were about 1 hour out on a 2.2-2.5 hour flight from DVT to ABQ. We decided to turn around, since we were less than an hour from sunset, and we wouldn't be able to take-off from ABQ with an inop alternator.

We still had one of the 70-amp alternators working, so we weren't in any kind of trouble, we just needed to be conservative. ABQ center and PHX tracon were very helpful, every new controller asked us if we needed any assistance or priority, but we always declined.

We turned off both GPS's and COM 2 & NAV 2 and tracked the airway in until DVT was in sight, then tracon gave us direct DVT. We landed at the end of twilight, but we had the panel lights off and the strobes off, kept the nav lights on and turned on the landing lights on short final. I shined the flashlight on the panel, mainly on the airspeed indicator. I can't remember every breaker that we pulled. I went to each breaker and we decided if that equipment was needed or not. We pulled the breaker on things like the starter, ventilation, electric trim, pitot heat (there wasn't a cloud in sight). We kept the transponder on, it only uses 5 amps and it gives us a second set of eyes in case something else happens.

We were under the 70-amps that the one alternator could produce. But if the other should fail, we'd have about a half hour of battery juice if the battery was in perfect condition.
 
I really don't see the need to turn everything off in a Seminole if you loose an alternator. As long as the other alternator works and you are below 70 amps, leave it on. Why fly around with a flash light in your mouth if you don't have to? Same thing with circuit breakers. The only reason to pull one is if you can't turn something off any other way. If you decide that pitot heat uses too much power, just turn if off, no need to pull the breaker. Same thing with the starters. They only draw power when you push the switch.

Some things like the turn coordinator can only be turned off with the breakers. If you are having trouble getting started on a cold morning, pull the breaker and make sure everything else is off. It can be the difference between getting started and having to get plugged into external power.
 
Heya,


Yeah, primary target is enough. The way I see it is if you have an electrical failure, let ATC know what's going on and what your plan is so if they loose you then they know where you are headed.

If you're in IMC when the electrical failure happens I'd want to get on the ground as soon as possible. Once you loose that last nav radio your chances of making an approach into somewhere go down and quickly at that.

In IMC my first worry would be navigation. You know that your gyro's are going to keep spinning if they are vacum powered (save for an electric HSI), so staying upright is not a big deal.

At least that's my reasoning.

Cheers


John Herreshoff
 
Assuming radar is available another option is to use your transciever as a reciever. In my experience, transmissions from the portable antenna are very poor, and ATC probabally would not be able to make out your transissions on the portable without the use of an external antenna. For rentals, this is not an option. So what you could in the worst possible scenario (i.e. you do not notice the failure until all the juice is gone AND you are IMC), is call up the FSS on a cell phone, tell them your plight and ask for vectors via your transciever 'reciever' and a PAR or ASR approach. Even in THE worst, worst case, IMC in a non radar environment, you could ask for a heading and altitude to the nearest VMC via a cell phone.
 
I'd leave the transponder on. If you have enough power to receive, but not to transmit, ATC can tell you to "IDENT to acknowledge" their instructions.

And the transponder provides a lot more useful information to ATC (so they can help you) than a primary return does.
 
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