What is a GPU (Ground Power Unit) Cart Start?

What is a GPU (ground power unit) cart start? Why does the subject of a cart start come up? Why do we need a cart start?

So we are flying a new old plane to the Bahamas.  My hubby has hours upon hours in a Baron but only a dozen or so in this particular one. Every new plane has her nuances.

This Baron is a little testy. Her engines run beautifully and are balanced.  Her oil burn is even on both sides. Her engine temps are on point.  She is a true thing of beauty.

However, when you turn off the engines and then try to restart her a few minutes later (like after clearing customs in Eleuthera), she is a bit cranky. When you add some oppressive heat and sitting on a hot ramp, to some very hot engines, she does not want to start.

Why would you need a GPU Cart Start?

We are hoping to get one engine started so we can turn on the alternator or generator on the running side to pull power to start the other engine. We keep trying but after multiple attempts to start her engines, we are out of luck.

If you try too many times to start your engines, even switching sides, you can flood an engine or kill the battery.

In our case, after a couple of attempts, the battery says – hey, I have had enough and dies. Yep, no power means no starting engines.

When you cannot no longer get enough power to get her engine to turn over, much less start, then you move to other options.

Now what?  

Suffer through staying on the beautiful island of Eleuthera and miss the experience of Black Point on a Great Ghana Cay?  Skip out on getting chased by another group of pigs and seeing some iguanas?

Nope, staying here is not an option. We like Eleuthera but a testy engine and now dead battery is not going to ruin my ability to explore other islands.   

What is a gpu cart start?

Per my pilot, it is time to request a cart start. What is that? (I wonder as the #rightseatpilot) This is a new term for me.

Well apparently there is a big ole set of battery cables that a lineperson can hook to your plane and jump you off. Some are their own carts and other are mounted to a golf cart. Thus, cart start.   

I know my extremely technical explanation helps, but at this point, you do not ask the pilot in command for more info. Dead battery, engines that do not start, plus oppressive heat equals very grumpy pilot.

The technical explanation is that a GPU is ground power unit. A GPU cart start is a electrical power generator that can start or run electrical elements of an airplane.

A ground power unit cart start should not confused with a cartridge start used on radial engines or a huffer cart start in jets.

You can use a GPU cart start for smaller general aviation airplanes, if you have a dead battery. If your plane has an electrical air conditioner, you can use a ground power unit to run the air conditioner while sitting on the ramp. You can also use the the power supply to run control systems, flight instruments, and radios for communication.

Larger airplanes, such as jets and turbo props, often use a ground power unit to run the air conditioners, refrigerators and other electronics while sitting on the ramp.

Our maintenance shop uses a ground power unit to run the planes during maintenance. My pilot says the only way to control aviation costs is to control the cost of maintenance. Running electric systems and avionics with an external power source for installation, repair and testing is much easier than having to run the engines.

The good news is fifteen minutes after the request for a cart start, the ground power unit arrived and the extremely testy engines are running smoothly. The cabin temperature has cooled dramatically, now that we have some altitude and left the sweltering ramp.

The pilot and passengers are now in flight to Great Guana Cay.  Everyone’s mood has improved, especially the grumpy pilot. Though the topic of conversation is how to avoid a repeat issue on our return flight.

This #rightseatpilot is plotting the first drink on the beach and imaging the the feel of crystal blue water lapping over my toes. The passengers (all children) are counting down and planning their dash to the water upon landing, while arguing who will get there first.     

Incidents Happen

No trip is ever routine, which us why we always take the safest route and carry all the necessary supplies. When we travel over water, we stop at airports that offer services if possible. My pilot, who is also an A&P brings a few tools along for the ride.

So many of the out island airports do not offer any services, so we are lucky the engines complained at Eleuthera and not at our final destination for this flight.

Life continues to be an adventure and we love every minute of it. Even when things do not go as planned, we consider it part of the fun.     

FAA Requirements

The Federal Aviation Administration has very little information published on ground power units. A policy handbook references ground power unit and can be read here.

*Update

My trusty pilot did some research and found a method to beat the finicky engines on a hot start.  A couple techniques with the engines and she started up beautifully. Clearing out in Eleuthera did not require a ground power unit, though I think we were all hoping to get ‘stuck’ in the Bahamas.   

Cart Start Adventure

Have you needed a GPU Cart Start? Any experience with testy engines? Tell us about your experience. We want to hear about it.  Email us.

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