I have for some time advocated against jump starting an airplane battery because you damage the battery, or end up loosing all electrical power.
I once jump started a C172 prior to a VFR flight from Hamar to Kristiansand, way back when I was young and reckless, being sure that the alternator would charge the battery enough so I could get the engine started before departure from Kristiansand. After takeoff I entered the Oslo TMA, and was in radio contact with Gardermoen Approach (that’s what they were called back then). West of Oslo, around Hønefoss, I decided it was time to turn on the anticollision lights that I had left off at departure, and immediately lost all electrical power. So now I had no radios, no transponder, no handheld. But I had a GSM phone (one of those big ones you could not fit in your pocket) that I used to call Gardermoen, explained all was well and I would proceed NORDO to Kristiansand.
And I did. Approaching Kristiansand I followed the NORDO procedures that consisted of circling at some defined spot on the coast and wait for light signals. Since I had a phone, I called the tower who have me a runway and cleared me to land after a B734. There was a cell in the vicinity. I set myself up for a base and final to the runway and landed safely, although in a tailwind that made me come in high and float quite a bit down the runway, so much so that I was close to initiate a go-around.
Tower was not happy that I had chosen to land at a “busy” airport without radio (those who have ever been to Kristiansand know how “busy” they are, and imagine what it was in those days). My rationale for continuing the flight was
Anyway, this is one great lesson that I had actually completely forgotten until I read this AvWeb article which I found while researching a completely unrelated topic. It contains a bunch of good reasons not to jump start, especially TAA (Technologically Advanced Aircraft – ie. glass panel aircraft).
An interesting story. But what is the relation with jump-starting? Had the outcome been any different if you had started by hand-cranking?
What I do find, errm, less clever, is that you took off without ever investigating why the battery was flat – neither do you mention what the volt- and ampmeter said, even before take-off. If those read normal, I too would have assumed the battery would charge allright.
BTW I am curious how the switching on of a relatively small load could provoke a total loss of electrical power – surely there was more wrong than met the eye?
[[edited after reading through the linked article, though not in depth]] As I read the article, it it does not warn against jumpstarting as such, but rather against an immediate take-off after jumpstarting. That does make a lot of sense.
I took the family to Dryreparken from Stavanger a few times years ago in a Sola Flyklubb C172 or PA28 and we used to land at Kristiansand….so have great memories of the place!
In terms of jump starting (via the external power socket of course) a G1000 aircraft I think you’re probably right…you can’t start up and then switch on the panel….but for non-glass I don’t see a problem….I’ve done it quite a few times .., just remember to have everything switched off….some people even pull all the breakers…. But my mechanic would probably agree with you…he would remove the battery and out it on a charger….
And I have some difficulty when I read in that article that a DA42 has a primary battery of only 10 Ah, even at 24V that makes a mere 240Wh – my Rotax 912 has 17 Ah for 200 Wh to start from, though I admit that was choosen on the ample side, deliberately. Hadn’t I heard diesels require a lot of power to start, with their much higher compression ratios?
Jan_Olieslagers wrote:
An interesting story. But what is the relation with jump-starting? Had the outcome been any different if you had started by hand-cranking?
It would have amounted to the same thing. Using external power merely allows you to use your electrical starter motor and excite the alternator so it starts generating current. Actually, later that day someone helped me start by hand-cranking so I could get back – with the anti-collision lights OFF.
Jan_Olieslagers wrote:
What I do find, errm, less clever, is that you took off without ever investigating why the battery was flat – neither do you mention what the volt- and ampmeter said, even before take-off. If those read normal, I too would have assumed the battery would charge allright.
But that was kind of the whole point with the story. And you cannot know for sure whether the battery will actually charge, which is one of the points made by the article. And as to the readings of the ammeter and tension (volts), it was 20 years ago, so I have to give myself the benefit of the doubt and assume I would not have taken off if they did not read correctly. And the alternator must have produced power, otherwise I would not have had any radios or transponder. The fact the the ammeter shows evidence of a positive charge, does not mean that the battery accepts/keeps charge…
Jan_Olieslagers wrote:
BTW I am curious how the switching on of a relatively small load could provoke a total loss of electrical power
It seems like charging the capacitors that thereafter discharge to flash the anti-collision lights creates a spike of load. That was enough to trip the ALT C/B, and once it was tripped the battery which I assume did not have enough current to excite the alternator field.
I do it all the time usually because someine left the master switch on and I’ve never run into problems.
Put in enough charge so the alternator will work and then either hand swing or jump start the engine.
Keep the electrical load to a minimum which at an uncontrolled airfield where I’m based isn’t a problem and after an hour flying it’s fine.
Yes in an ideal world we trickle charge it overnight and from time to time we do but usually we don’t have the time.
Well, there IS the danger that the battery does no more hold the charge, indeed.
Still, I think the title of the thread (and of the article referred to) are very confusing: there is nothing inherently wrong with jumpstarting.
Frankly, I don’t even see what difference it could make for a glass panel, even if electronics are of course more delicate. But during starting one switches off everything electronic anyway, only to switch it all on after the voltage has stabilised.
Come to think of it, briefly switching on all the big loads (pitot heater, landing light if not LED, …) before take-off might be a good point to add to one’s checklist, it might have avoided @Aviathor’s incident. A pity one can’t include gear retraction… that caused a similar accident at my homefield, several years ago.
Good topic.
I think it is OK to jump start IF one is sure of why the battery went flat e.g. you left the master on for a number of hours.
Also, you can see how the battery charge is coming along, from how the charging current is dropping.
Obviously I would not depart into IMC or dodgy wx without a fully charged battery.
And having one’s own plane, and being involved in the maintenance, improves the situation dramatically because you know it well and know the history.
There is a separate issue here: there is a specific jump starting procedure for different aircraft types, depending on how they are wired. This should be in the POH and if you don’t follow it properly you can blow some fuse(s). Here is the one for the TB20GT
Brakes: ON
Battery Master: Off
Alternator: Off
Avionics & Autopilots Masters: Off
All other Electrics: Off
Connect External power cable
Note: NEVER turn on the avionics master switch with the engine running unless the external power cable is removed and the battery master is on.
Battery Master: On
Start Engine allow it to stabilize
Battery Master: Off
Remove External power cable
Battery Master: On
Alternator Master: On
Allow engine to warm long enough so it will idle correctly
Battery Master: Off
Landing Light: On
Taxi Light: On
Engine RPM: Idle
Battery Master: ON
Bring Engine RPM up to 1500 RPM
Check that the indication of the factory voltmeter stabilizes inside the green sector. If the voltmeter is in the lower red sector, shutdown, remove and charge the battery before flight.
Landing Light: Off
Taxi Light: Off
Proceed as per normal checklist
One of the things I have noticed when occasionally assisting with a jump start, is that the ammeter starts out showing a very high current, consistent with the max output of the alternator (70 amps), before it progressively reduces to more sedate 30 A and below. But that cannot possibly be good for those small batteries with tiny, thin lead plates, worth 600-700 € and which already have a limited lifetime without being abused.
Sorry, but again: would it be any different when hand cranking? It says nothing about jumpstarting as such. Also, the very high current can only last for a short while, it cannot be so very bad. Yet I agree it is better if one can (at least partially) recharge the battery with a charger, before starting the engine in whatever way. @Bathman hinted the same.
