Installing USBs in BizJets: An Unexpected Challenge

Aircraft owners choosing to install rapid-charging USB ports at each passenger seat are creating a trend that has important implications for aircraft electrical power-generation requirements — both in itself, and in what it could presage for future aircraft power needs as new technologies make their way into the cabin.

One of the most noticeable trends in Business Aircraft cabin refurbishment today is for owners to ask MRO providers to install rapid-charging USB ports at every passenger seat in the aircraft, to allow passengers to use their personal electronic devices in flight and keep the devices fully charged.

These installations are often accompanied by similar installations of USB rapid-charging ports on the flight decks of the aircraft, as owners and pilots replace traditional flight bags with lightweight, easy-to-use, easy-to-access tablet devices.

Moreover, aircraft owners usually want installations of dual ports, rather than single ports, at each seat and pilot position, according to Duncan Aviation’s Avionics Sales Representative Adrian Chene.

Also notable, according to Bill Stone, Senior Manager for Aviation Business Development at Garmin International (a leading manufacturer of aviation-grade USB charging ports), is that owners usually choose to have the most powerful USB rapid-charging ports installed, rather than the less powerful ports that the manufacturers also offer.

The desire to install dual USB ports at every passenger seat is a natural one for owners when passengers in Business Aircraft cabins increasingly are consuming personally selected video, graphic and audio content by means of their PEDs, rather than everyone watching or listening to the same video or audio content at the same time, on bulkhead monitors and whole-cabin sound systems.

USB ports at each seat not only provide each passenger with individually tailored entertainment and communications, but also the major convenience of keeping each passenger’s PED batteries topped up to allow immediate use when the passengers disembark from the aircraft.

However, there is a cost associated with the increased individuality and convenience that USB ports at each seat provide.

The direct cost of installing certificated aviation-grade dual USB rapid-charging ports at each seat is not major in terms of the notoriously expensive business of buying and installing aircraft equipment. But neither is it insignificant...

Such units — which, unlike ordinary consumer USB ports have hardened, specially tested electronic circuits to ensure they do not create radio interference with flight deck avionics and radios, and are designed specifically for use in aviation environments — are priced at around $300 each. And they require installation, at a price, by an MRO provider which knows what it is doing.

Indirect Costs of Installing USB Rapid-Charging Ports

Just as importantly, there’s also an indirect cost associated with installing USB ports — one to which many owners may not have given much thought, but which could be a concern, particularly for owners wishing to retrofit older business aircraft with USB data feeds and rapid-charging capability. 

That cost is the increased electrical power requirement demanded of the starter-generators associated with each engine, to produce the sizable amounts of power that dual USB rapid chargers need.

Stone and Chene note that the additional peak USB-port electrical power requirement, plus the existing electrical-power requirements for the aircraft’s other flight deck, control, systems and cabin functions, must lie well within the specified electrical power-generation capability for which the aircraft is type-certificated.

Simply put, to provide a sufficient margin of control and safety in any foreseeable operational situation, type certification rules for any aircraft require the maximum potential consumption of electrical power by all the aircraft’s systems to be no more than 80 percent of the aircraft’s certificated electrical power-generation capability, according to Stone.

That said, Chene notes different aircraft manufacturers have different methods for calculating the peak electrical loads and requirements on their aircraft, which in practice might stretch the 80 percent limit by a few percent.

The arithmetic by which the maximum power requirement for the aircraft’s USB ports is derived is simple. As an example, Chene posits a retrofit with dual USB rapid-charging ports at all 12 passenger seats and the two pilot seats in a Dassault Falcon 900EX, which (like all other modern Falcon models) is designed largely to use DC electrical power rather than AC power.

When charging personal devices, aviation dual USB rapid-chargers can draw peak electrical input loads of 60 watts or more per port. (Garmin’s GSB 15 dual-port USB Type A units draw a maximum of 68W per port, while each of the two ports in Mid Continent Instruments’ TA360, another widely used aviation dual USB rapid-charger, draws a maximum of 60W.)

Stone notes that such peak input loads last only for very brief periods, because the device being charged controls the level of power draw and can only handle the peak input power level for a short time, reducing the draw quickly from that level as its battery becomes more fully charged.

But Chene points out the overriding factor in calculating the aircraft’s total electrical-power requirement is that the aircraft’s type-certification rules require that, no matter how unlikely it would be for everyone on the aircraft to be charging devices through two ports at the same time, the starter-generators must be able to provide (say) 68W x two (USB ports per seat) x 14 seats, for a total of 1.904kW.

At the same time, the aircraft’s starter-generators must also provide enough power for all the aircraft’s other electrical requirements.

On top of that, to meet the type-certification requirement the total of the theoretical power in wattage required by all the USB ports, plus all the electrical power required by all the aircraft’s other systems, must come to no more than about 80 percent of the total electrical power-generation capability the aircraft’s starter generators provide.

Replacing the Engines’ Starter Generators

A new, additional power draw of 1.9kW might not sound very important, considering that in aircraft whose starter-generators are designed to provide AC power (in other words, most older aircraft), AC inverters each consuming 1,200W-2kW of power are used to provide DC power to heat coffee pots and coffee makers, and other AC inverters on board provide power for flight deck avionics units. 

It was “very common” for aircraft built 20 years ago to use powerful AC inverters to provide 110V power to the cabin, according to Stone.

Now USB power is taking over. And the fact remains that supplemental type certificates (STCs) exist for various business aircraft type — particularly turboprops such as Beechcraft King Airs and possibly smaller, older business jets — to provide more powerful starter generators to replace the starter generators with which they were originally fitted.

According to Stone, early-model King Airs were fitted with two 200kW starter generators, one per engine, but over time the standard grew to 250kW starter generators.

For special mission needs (many King Airs are used for government and commercial special missions), the total electrical power requirement “vastly exceeds that” 400kW or 500kW total, and STCs now exist to provide King Airs with two 400kW starter generators, says Stone.

The development of STCs for replacement starter generators resulted, at least in part, from a long-term trend from the 1960s through until relatively recently. That trend was for new and older aircraft designs alike to require more electrical power, as electronics capabilities which were developed for the consumer market increasingly found their way into aircraft cabins.

“It was the same with houses,” Stone notes. “It used to be you needed 80 Amps to power your house, and now you need 200.”

Starter Generator Replacement – How Much?

It is now “very common” for owners to have USB ports installed on flight decks and in cabins when they induct their aircraft for avionics upgrades, “for Cessna 172s and everything up from that,” Stone notes.

In every case, no matter what the aircraft type, the MRO shop has to perform an electrical load analysis to ensure that the electrical power requirement for the USB ports doesn’t tax the aircraft’s power-generation system to a level beyond that allowed by the aircraft’s type certification.

If it does, the aircraft owner must be prepared to trade off existing cabin electrical requirements against the desired USB rapid-charging capability or pay the cost of performing a starter generator replacement, downsize in scale, or forgo completely, the planned installation of USB rapid-charging ports.

When ordering a retrofit, the owner must take pains to know just how much accomplishing the relevant starter generator replacement STC will cost, particularly when the aircraft in question is older or otherwise has a relatively low residual hull value. In some, or many, cases no starter- generator replacement STC is available at all.

Indeed, Chene recently asked one business jet manufacturer how much its starter-generator replacement STC would cost to perform, and the OEM replied that it had never received a customer request to develop such an STC.

But where an STC is available, the cost of having the replacement starter generators installed is always expensive — and particularly significant for any owner whose aircraft is worth only a few million dollars in the first place. Chene explains that any replacement STC is “highly likely” to require replacement of the starter generator in each engine on the aircraft, not just one engine.

For all sorts of operational, safety and maintenance reasons, it would be inadvisable to replace the starter generator for one engine but not the unit for the second or third engine. That would result in the power draw from each engine being different, potentially creating an unacceptable flight-safety risk.

Should an STC for replacing the aircraft’s original starter generators be available, the owner should be prepared to receive a bill from the MRO shop for $300,000-$400,000 to cover the cost of the equipment and labor, says Chene.

For the sake of gaining a few USB rapid-charging ports, such an investment could easily prove more than the owner of an aging Business Aircraft might be willing to bear.

Stone reckons the trend toward increased cabin electrical-power usage has now flattened out and he sees it basically remaining similar to those of today as updates of existing cabin electrical and electronic technologies are introduced which use the same (or less) power as today’s technologies.

He says LED cabin lighting is a good example of a modern electrical technology now becoming prevalent in Business Aircraft cabins which uses less power overall than predecessor cabin lighting systems.

Why not complete this series and read Future Cabin Technologies: Is Your Jet Ready? concluding the way that future cabin electronic technologies could change the cabin power usage picture will be discussed, along with how owners and operators can prepare for these changes.