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Comment by crazytony | Hacker News Reader

Yep. The air transport industry is very very change (read: risk) averse.

The current APUs (except for 787) have traditionally supplied power at 28 VDC and 115 VAC due to the worries about high voltage arcs. They would rather have more current over more copper than higher voltage.

I suspect they have added significant wiring and electronics to this A320 to get this to work. I haven't been able to find out if this aircraft has even flown with this rigging much less gone through certification.

I bet they could slightly improve this system and get rid of reversers as well (active braking).

That being said, I'd imagine ATC to be very wary of the current 130hp system: there is no way you could expedite a move across an active runway at almost 80,000kg MTOW.

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I imagine that the APU generator must be reinforced or redesigned to be able to withstand the charge of the motors. Revereser are quite efective and I don't think you can get rid of them, because when you have slippery runways the braking through the wheels is going to be compromised.

It's also another sys to fail on toP of the normal braking system (that already has quite a bit of it's own problem), so it's better to have paralel systems for the same function.

If you are going the active braking route you'll need a place to send that electricity and the actual batteries are not big enough for that.

You are right that the motor are not very powerful, 20kts max is a bit on the slow side as top speed. Given that in a big airport when you taxi at less than 15 kts you are slowing the rest of traffic (and they get nervous indeed when they are following a turttle!). Also to really be autonomous with this sys I imagine they'll install cameras to see the rear and the engines's nacelle (to be able to see that the engine is starting without issues, witha normal pushback you have ground crew observing). That's another level of systems that need new procedures and testing, not very complex initially but things can become really weird very fast in aviation and all unusual user cases must be taken into account.

Edit:phrasing correction

I think it's an oversimplification to say the reason for this innovation not happening sooner is because of risk. The Boeing 777 flies on only 2 engines which sounds far riskier but didn't stop it being approved. Also there's a race for building planes from carbon materials.

Robert Witwer, vice-president of advanced technology at Honey-well of Morristown, cited some other reasons [1]:

- Increased congestion: "Short hauls do a lot of taxiing time, especially in a place like Newark, where you can be 20th in line"

- Legislation: “And there are a number of airports in Europe that have tough emission standards that would make the Green Taxiing System appealing. I believe it’s a game-changing technology."

- Fuel costs: "The prospect of annual savings of $200,000 per jet from lower fuel use and less ground time has sparked interest from Airbus and airlines such as EasyJet and Alitalia. Airlines face the highest sustained prices ever for jet fuel. United Continental, the world’s biggest carrier, says it burns $25,000 of fuel per minute. Jet fuel delivery in New York averaged $3.12 per gallon in 2012, more than four times as much as a decade ago."

- Technological advances: "What’s new in today’s technology is the convergence of airlines’ search for more efficiency and recent advances in miniaturizing electric motors to propel a plane at the 32 kilometres per hour it may need for taxiing."

[1] http://www.wingsmagazine.com/index.php?option=com_content&ta...

It's more like risk vs gain. There was a lot of testing and previous experience leading up to the 777 launch ETOPS rating. A better example is the 787 battery system. Likewise, you want to be very certain that the new electrical motor system won't interfere with normal braking, so something that sounds simple becomes very complex and difficult once you put it on an airlplane.

It sounds risky to operate with only 2 engines, and in 1953 twin engine planes were only allowed to be within 60 minutes of a diversion airport, mostly because of the unreliability of piston engines. It was a fairly long journey to allow twin engine planes to fly the kinds of routes they are allowed today. http://en.wikipedia.org/wiki/ETOPS

As jet engines turned out be much more reliable than their piston counterparts, the restrictions were loosened over time, starting with waiving the 60 minute rule for tri-jets in 1964. The original concept for the 777 was actually a tri-jet design. However the 767 turned out to be very reliable as a twin-engine plane and in 1985 it became the first twin engine plane to be allowed to fly 120 minutes away from a diversion airport (ETOPS-120) and in 1989 it was allowed to fly 180 minutes away from a diversion airport (but planes had to first complete 1 year with 120 minutes before they could be certified for ETOPS-180). Since twin engine designes were suddenly much more capable than anticipated Boeing dropped the tri-jet design of the 777, and eventually came back with a twin-engine design. By 1995 there was enough experience with operating twin engine planes with the 180 minute rule in place and Boeing was able to get the 777 certified to 180 minutes from the start.

So it basically took from 1953 to 1995 to allow a brand new twin-engine plane to fly most transoceanic routes (with a 180 minute rule in place), based on increasing evidence that the jet engines themselves are fairly safe, and learning more about additional safety mechanisms and procedures required to safely operate twin engine planes at extended distances from diversion airports.

Great post, thank you.

The video at the bottom of the OP shows that plane taking off and landing.

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