Cold Weather Special: What Are Some Of The Major Challenges in Using Diesel GPUs In Cold Climates?

Well, 2023 is behind us, and we are firmly in January, which means it’s cold out for about three-quarters of the U.S. Cold weather is great for flying, but it’s terrible for equipment. While the summer is harsh and hard on equipment, sub-zero winter operations are arguably far worse. Oil is thick, meaning machines will run for the first couple of seconds with suboptimal lubrication, metal becomes brittle, and batteries drain to nothing. 

The most common source of 400 Hz power to aircraft remains the venerable diesel ground power unit, a piece of equipment that has remained largely unchanged for decades. While these have proven overwhelmingly reliable, they don’t come without disadvantages. 

Diesel engines have come a long way for winter operations, but they are still occasionally finicky and hard to operate in the winter. Let’s take a look at how winter operations impact diesel aircraft ground power units and if they are still a reliable provider of electrical power for aircraft.  

An Introduction to Ground Power Units (GPU)

While all general aviation aircraft and most corporate turbine aircraft are able to operate and conduct pre-flight checks on battery power alone, almost all tactical military aircraft need external power, and all heavies require it. 

The standard is generally a 400Hz system selected because of the relative weight of components. Weight is the primary determining factor of every single item that goes into or onto an airplane. In short, an electrical motor the size of a watermelon could be replaced by one the size of a 16 oz coffee can (a great analogy from FCX Systems).

A U.S. Air Force Airman pushes a GPU in Alaska.

Airliners require enormous amounts of electrical power to function on the ground before generators are turned on, and the simplest way to do this is through a ground generator unit. Diesel engines have long been the ideal solution for generators for a couple of reasons:

  1. Enormous torque-to-weight ratio
  2. Far better fuel economy than gasoline/petrol
  3. Diesel engines are built to operate best at fixed RPMs for long periods of time (think of over-the-road trucks)

In terms of both portability and cost-efficiency, a diesel aircraft ground power unit is almost always a more cost-efficient way to provide electrical power to the aircraft electrical systems instead of the extremely high cost of installing permanent 400 hz power generation aircraft systems for power supply.    

Why Diesel GPUs Are Still So Common

Relatively speaking, it is still much cheaper to buy diesel ground power units than to build up the infrastructure to have dedicated 400 Hz power at every jetway (although some places do). Also, traffic count is an important thing to take into consideration. 

Everything is an investment in your aircraft ground support plan, and selecting a ground power unit is an important one. If traffic counts can’t justify infrastructure improvements to provide electrical power pits at every spot, then a diesel ground power unit is really the only other feasible option. 

And besides all that, they are still extremely reliable and do the job well. They are relatively simple, and once they are warm and running, they are still completely effective in all weather conditions. The key word here is once they are warm and running. 

Diesel Power Units Are A Robust Choice, but Not Without Challenges

Industrial diesel engines have powered just about anything you can think of for decades, from backup generators at hospitals and other critical infrastructure to forklifts, trucks, tug boats, and road graders. You name it, and a diesel has probably powered it. 

Diesel engines have improved radically in recent years and are night and day different from where they were even a quarter of a century ago. However, they are also substantially more advanced and complex engines than those of yesteryear. A modern diesel engine is incredibly advanced, relying heavily on digitization for its operation. 

While more reliable, this also means more upkeep. More upkeep means more expense for ground power units. 

Winter Ground Operations Challenges

Now that we have talked about the diesel ground power unit ad nauseam let’s talk about winter flight ops. 

Winter flight operations are some of the most demanding ground support equipment and aircraft systems. It is hard on the mechanical components, and it’s hard on the electrical components. The power supply is crucial to keep the systems online and fully functional. 

For one thing, it is one way that the batteries stay fully charged. Of course, the battery has to be charged to a certain level before it can be applied, but assuming that threshold is met, the power supply charges the batteries so it is fully charged and available for flight ops.  

Cold-Start Woes: Starting Challenges in Frigid Weather

Diesel engines are notoriously hard-starters during the winter. It has always been this way, although modern diesel engines do not need to be plugged in until the temps drop below freezing. Also, until the weather is extremely cold, the engine block remains warm for an hour or two and usually gives no trouble restarting within that window. 

Another major struggle with diesel engines is diesel fuel gelling. And here’s the thing: once that fuel gels, it doesn’t matter how warm the engine is. When the fuel gels, the lines clog, the filters clog, and the engine starves. Adding fuel anti-gelling agents is a common aircraft ground power unit maintenance task. 

Remember, though, anti-gelling agents do not help the aircraft ground power unit to start any easier; they simply keep the fuel from turning into a solid.  

Strategies for Enhancing Diesel Aircraft Ground Power Units Performance In Cold Climates

Alright, so we come to an impasse here: in very cold climates, a hangar-powered ground power unit (or one hard-fixed into the pavement) is probably the best bet. However, because of the high cost of installing these systems, they may not be viable. 

If this is the case with your operation, you should consider how to keep your diesel GPU ready. 

Also, recall that this is about more than just the engine starting during the cold. It is also about whether or not it will crank during the cold. 

Engine block heaters on diesel engines are the first line of defense. They draw about 1 Kw, and they should be used only when the GPU needs to be ready for use. Installing industrial-grade timers can help keep energy usage to a minimum for pre-heating, as the block heater only needs to operate for about three hours before engine start (one the GPU, not the aircraft engines). 

Another consideration is battery preservation. Cold weather accelerates the rate of gradual discharge because the chemical reactions are slowed, and as is well known, a battery is just a controlled chemical reaction. Once the diesel engine is up and running, the charging system will keep the battery charged up, but in the meantime, a trickle charger on each GPU is very cheap insurance against a fleet of generators that need jump starts when flights are on final.    

Best Practices for Diesel GPUs in Sub-Zero Environments

There are a few best practices that will keep your GPUs running well in cold environments. With proper care, diesels are great in the winter; just look at the interstates. You don’t see the tractor-trailers and Hot Shots stop running in January. 

Maintenance Matters: Keeping Diesel Units Reliable in Freezing Conditions 

Diesel GPUs generally use engines that are practically the same as found in diesel automobiles. A diesel engine does what it does well, and there is no reason to reinvent the wheel between industrial water pumps, generators, or trucks and buses. 

Because of this, diesel GPUs today are much better than those of 20 years ago in cold weather conditions. But they are still not perfect, so here are some tips:

  • In the GSE staging areas, install power points that supply electrical power
  • Use these power points (standard 120 VAC) for trickle charges and block heaters
  • Keep the block heaters plugged in and on timers
  • Make sure that all diesel fuel supplied to your fleet is either already graded for the temps you operate in or have your GSE fleet maintenance team add anti-gel to it.    

Operator Training and Preparedness for Cold-Weather Diesel Ground Power Unit Operations

Winter operations are not like the rest of the year. Extreme cold takes a severe toll on all machinery, and if it is not operated properly, machinery can be damaged, and power needs will not be met. 

Make sure that your organization develops an SOP describing exactly how to use the aircraft GPU fleet to provide clean power to aircraft. Always remember that larger aircraft will need a diesel GPU for their needs, and battery-powered GPUs are a poor solution for larger aircraft and winter operations. 

You may have team members tasked with operating AGPUs who aren’t familiar with operating diesels at all, let alone during the winter. Bring all employees up to speed on the importance of: 

  • allowing adequate warm-up periods (ALWAYS abide by the 5-minute warm-up and 5-minute cool-down periods on AGPUs), 
  • plugging in block heaters when temps stay consistently below freezing (the operator’s manual dictates), 
  • NEVER use ether/starting fluid on a diesel engine. It’s better to put a charger on it or take it to the GSE shop, or call out a tech than to attempt starting with ether. Ether is a great way to grenade your diesel engines, so don’t even think about using it. You will destroy your engine. 

If the diesel engine glow plug systems are working properly and the battery is properly charged, and especially if the block is heated, there is no reason to use ether for engine starts. If these conditions are all met, and the GPU continues to resist starting, there is a problem somewhere in the pre-heating system that needs to be troubleshot, not an ether shot. 

Greenwood Aero’s Dedication To Ground Support Equipment

Greenwood Aerospace understands the importance of aircraft GSE. For one thing, AGPUs save considerable wear and tear over the use of auxiliary power units, not to mention fuel costs to provide AC power for electrical energy. 

Cold weather can wreak havoc on machinery, and diesels are the primary power source for AGSE in the modern day. When GSE breaks, you need to know that you can rely on us to procure your parts quickly. Also, if you are looking to source a reliable contractor for your aircraft GSE fleet, look no further than Greenwood Aerospace!

You can start with an online quote or call us, and one of our professionals will assist you with whatever you need to get started.