Taxi in on one engine
 

On a recent Flybe flight, I noticed we taxied in on one engine. I know this is common place with EZY, but I assumed in the airbus the SOP would be to have the APU running to do this?

My understanding of the dash would be that you need AC power for the hydraulics to work. With only one engine, you are relying on that one generator for your hydraulics, it would only have to click off and you would have no steering at all.

Have there been any cases where hydraulics have been lost during the taxi in on one engine? It would only take one even small incident to wipe out any cost saved on fuel burn.

Why wouldn't they have the APU running on the Dash?

Do all dash 8 aircraft have an APU? I thought it was only an optional extra. Would it be required to be running for taxi on one engine?

Just wondering, since I fly a basic turboprop where taxi on one engine would be a big no.

All the Flybe Q400s have an APU, whether it's serviceable or not is another question!

Maybe a current Flybe Dashist will be along shortly to give you the low down but I suspect that a single engine taxi will require the APU to be running.

There are engine driven pumps too, one engine running, was it #2?

Steering off #2 Hyd sys.

And the APU only has DC gen so makes no different for running AC Hyd pump

The Dash 8 has two different main electric systems installed.

Firstly, there is the variable frequency AC system that generally feeds high-load systems like probe and propeller heats, the galley ovens and also the #1 hydraulic system electric pump. The generators are connected to the propeller gearboxes and require the propeller to run unfeathered to provide power.

And secondly, there is the 28VDC system driving everything else ranging from avionics to cabin lights, and also the engine starter generators. This is powered by the two mentioned starter generators, when the respective engine is running, and the APU generator as well (usable only on the ground due to airflow issues inflight that prohibited the certification, or so I am told).

There are 4 hydraulic circuits installed, of which only the 2 main ones are relevant for taxi. Both have one dedicated engine driven pump which is found on the prop gearbox as well; in case of a pump failure, #1 is fed with the mentioned AC-driven pump and #2 leeches on #1 via a PTU if needed.

So the APU has no connection at all to the hydraulic systems and therefore is not required to be run for single engine taxi. Assuming #1 engine has been feathered (but running) during the case in question, its EDP would still provide nominal pressure, albeit at a lower flow rate. But even with #1 engine completely shut down, the electric pump would get its AC from the still working #2 engine and keep #1 hydraulic system and therefore the normal brake system fully serviceable. And #2 hydraulic is still fed by the unfeathered #2 engine and its EDP; typically the PTU is run during taxi as well to cover for contingencies.

At Tyrolean, we are encouraged to taxi with one engine in feather, as it keeps cabin noise down and also saves a drop of fuel. It comes with some operational caveats, but when one knows the pitfalls here, it is a reasonable procedure IMHO.