Four engined turbo-props

[ramsrc]

The other evening, I watched an Antonov AN-12 land at Frankfurt airport. As soon as the aircraft had cleared the runway, the two inboard Engines were shut down and the taxiing continued on numbers one and four. Which brings me onto my two questions.

Firstly, why is this done? Is it just to reduce fuel consumption or is there another reason?

Secondly, why the two inboard engines? Is there a manoeuvrability advantage, or is it purely arbitrary?

[PAXboy]

I am not a pilot but am a very experienced PAX, having been on flight decks many times and from a flying family.

What you saw is standard procedure on all multi-engine aircraft it just happens to be more visible on props!

On a quad, two engines will be cut once they have cleared the runway. This saves fuel but also (and more importantly) engine hours. Typically, the pair to be shut down will alternate by sector, Inboard/Outboard.

On tri-motors or twins, they may have different sequences. I do, of course, sit to be corrected. :)

[Nopax,thanx]

Very important to only shut down the engines which do NOT have the hyd pumps - or else you get no brakes, and a very embarrassed pilot (and I know someone who did it in a Herc!!!)

[411A]

PAXboy
I think you'll find the procedure varies amoung airlines, and is SCD. In addition, engines are not shut down immediately leaving the runway. Turbine engines require a cooldown period prior to shutdown.

[PAXboy]

411A, many thanks for the corrections. I guess that some carriers might prefer to always shut down the same engines and thus increase the hours so that engine changes can be staggered or is the amount of hours insignificant over the period between checks?

[ramsrc]

Thanks for the replies, but 411A's post has posed another question!

How long would the cool down period be before the engines can be shut down? The engines on the Antonov in question were shutdown very quickly after the aircraft had left the runway. It could not have been much more than 30-45 seconds after touchdown.

[BlueEagle]

Seem to remember two minutes at idle to allow for heat soak etc.
On a B747-400 you would only shut down one engine, #3, and that would be to save fuel or reduce residual thrust when taxying with a very light a/c thus keeping taxy speed down and saving brake wear.
#1 and #4 always required for brakes and steering, (assuming neither had failed!).

But, of course, a B747-400 is NOT a turbo prop!!!

[mustafagander]

A simple reason for shutting down inboards on a turboprop could be the time it takes for the engine/prop to spin down and stop turning. No matter how careful all hands may be, a spinning prop is a dangerous thing in a busy work area and for the exiting pax to walk close by.

[TR4A]

When I flew the C-130 I would shutdown the inboards for noise.

[MaximumPete]

On the Viscount 701 the hydraulics were on the outboard engines which meant that SOPs dictated that the inboards were shutdown at about 70kts during the landing run to avoid fuel dripping onto the brakes. It had it's moments, particularly in the dark during a cross-wind landing.

There was a prop brake to slow down the No 1 engine but I never saw it used. A heavy engineer seemed to do the trick.

We are looking at late 1960s here!

MP