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From smart phones to laptop computers to the iPad, portable, personal, and productive electronic devices (PEDs) have not only changed our daily lives, they have redefined the AC outlets found on Part 25 transport category aircraft. Even though PED plugs fit in old-school “dumb” outlets, FAA Policy Memo ANM-01-111-165, Policy Statement of Power Supply Systems for Portable Electronic Devices on Part 25 Airplanes, makes it clear that these outlets are are NOT approved for this use.
Most aircraft 110-volt AC outlets today deliver 500 volt-ampere power to whatever is plugged into them, like the cleaning crew’s vacuum cleaner. An iPad is not a vacuum cleaner. Like most PEDs, it has a lithium-polymer battery. Feeding too much juice to lithium batteries can lead to bad things. In thermal runaway a battery can deliver shocks, burns, and smoke. And overloading the PSS circuit can shut down the electrical bus it is connected to, and maybe even the generator that powers it.
To avoid these problems—and their consequences—the FAA requires “smart” PSSs that deliver “Goldilocks” power, not too much, not too little, just right for the PED’s operating needs. In a 1997 policy memo, the FAA said 100-watts adequately powered the laptops of that era, so it was the PSS’s max output. With the maturation and proliferation of the extended PED family, in 2005 the current memo doubled the power limit to 200 watts, still less than half that in dumb outlets.
In an AC circuit, the 200-watt PSS maximum is better specified in volt-ampere (VA), which is like a watt but not identical. Electrical engineers prefer the volt-ampere because it is the unit of measurement used in the selection of conductors and devices that protect a circuit. Regardless the measurement, the consequences of too much power are the same.
PEDs today have no “novel or unusual design features” that require specific mention of them in federal aviation regulations or requirements, says the policy memo. The current regs and requirements provide an adequate level of safety and the memo lists all that apply to the certification of a PED PSS. Dated March 18, 2005, the memo supersedes 1997 policy for the installation of in-seat power supply systems. The current policy covers all PED power supply systems regardless of the outlet’s location: the cockpit, seats, cabin baseboards, or a cabinet on the aft bulkhead.
Related regulatory guidance can be found in two other policy memos: ANM-100-2000-00105 (September 18,2000), Certification of In-Flight Entertainment Systems, addresses wire installation and cabin components, including “smart” outlets. ANM-111-2002-01-04 (January 28, 2003), provides guidance on wiring design and instructions for continued airworthiness.
Limiting the PED PSS to 200 VA prevents its use for unintended functions, like driving a curling iron or hair dryer. It is for PEDs only, and further guidance can be found in Volume 4 of FAA Order 89001, which covers electronic flight bags (EFBs). A tablet computer like an iPad, worn as a kneeboard, is a Class I EFB. Mount it in a bracket and it is a Class II EFB. Regardless, it is still a portable electronic device that needs power.
Of particular interest is section 4-1644E, Power Sources: When the iPad’s battery is the primary power source, aircraft power can be secondary, recharging the battery in flight. Continuing this thought, Section 4-1648A, EFB Power Source, points back to the PED PSS installation requirements. A note reiterates the safety hazards posed by over-charging or discharging lithium-ion batteries. “Operators should have lithium ion battery charging procedures which are in total accordance with the battery manufacturer’s charging instructions and prevent aggravation of lithium ion battery thermal hazards.”
With a “dumb” outlet that delivers a fixed flow of energy, this is easier said than done because every manufacturer has slightly different charging instructions. Some prevent overcharging by automatically reducing the AC input when the battery is topped off. Others tell the user to pull the plug when the LED stops flashing.
Therein lies the beauty of a smart power supply system like ASIG’s Astronics AES EmPower® system: it reacts to the load of the connected device and ensures against over-current, over/under-voltage, and frequency differential conditions. Once satisfied that the connected device does not demand more than these thresholds, it provides only the amount of volt-amperes deemed suitable for PEDs as established by the Federal Aviation Administration.
Naturally, there is much more involved in installing a power supply system specifically for PEDs whether they are video games, smart phones, or iPads. For more specifics, contact ASIG.
Until next time, stay 5x5, mission ready, and Wired!
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