A320 Ditching - Both engines out - What Electrics and what Slats/Flaps can deploy ?
 

Reference to the US Airways A320 ditching.

Can someone explain what electrics are available and what flaps and/or slats could be deployed with both engines failed (but still rotating) ?

Bit rusty on the 320 but emergency electrics will be available powering captains instruments and some flight control computers. The ram air turbine should have deployed providing pressure to the blue hydraulic system which would give leading edge slats.

Carnage is right, with the loss of both engines (AC BUS 1+2) the RAT should deploy automatically. On deploying it powers the blue hydraulic system, which drives the emergency generator by means of a hydraulic motor. This generator supplies the AC ESS BUS, and the DC ESS BUS via the ESS TR. This will result in P1 displays working and P1 comms working. As for the Hydraulics at low speeds (which you will be in the glide) only the blue Hydraulics will give pressure so you can deploy Slats only. The checklist though calls for you to move the flap lever to Flap 3 position incase of residule pressure giving a little more. Interestingly last time I was in the sim we were doing Dual Eng Failures from altitude and it was debated as to the merits of starting the APU, risk is that if you attempt a start and it doesn't start for some reason then you have severly reduced your available battery capacity. If it does start however then you regain electrics, possibly can start the Yellow Electric pump to gain full flap availability etc.

I don't fly the A320, but I suppose the "start APU" question comes down to whether or not, you see the battery as essential. In the NYC case, I doubt battery power was a consideration, assuming it isn't needed while the RAT powers AC ESS.

GF

Does anyone know if US Air keeps the APU on during take-off? (fuel costs being what they are it might but shut down after startup). I don't know the 320 as well as the 737 but having a running APU would give lots of AC power for hyd pumps and avionics.

Starting the APU would also allow you to try a restart with bleed air instead of only a windmilling start (plus you'll be able to slow down from about 300 kts for a windmilling start to GD for a bleed assisted start, thus increasing your gliding range), assuming you've got altitude and time.

Also, with the RAT out powering the Emergency generator through the hydraulics, you have more than only the batteries, so are they really that critical? I was taught to always start the APU with all engines out.

I am not A320 rated, but......

1. Surely battery power should be available for all electrical services...30 min minimum?
2. APU start following complete loss of all electric generation? Is that a recommended practice on the Airbus?
3. I cannot add to the debate about what hydraulic services may be available from the RAT as I do not know.

Pictures of the salvaged US Air A320 show flaps extended to what appears to be landing config. If so, the APU or at least one engine must have been running.

Attempting an APU start can drain the battery rapidly. If the start is unsuccessful you'll be left with a dead battery and electrical services dependent on the RAT. As the RAT will stall below about 140kts you could find yourself left without instruments or controls at the most critical phase of the flight. I'd probably consider one start attempt if at high altitude and time permitted, but with a max altitude of 3000 feet on the flight in question I think I'd have higher priorities than starting the APU if the aircraft was still flyable.

Retired now for a number of years but even then we did not use the APU after engine start unless there was an MEL requiring it. So, no.. the APU was not running on 1549.

What is the min IAS for windmill start on the A320 with CFM56 engines? I'm wondering if at 3000 feet and "green dot" speed a windmill start would be out of the question without the APU-assisted start.

GF

Regarding AH's comments above.

I understand the slats on the blue system, but with the flap lever in position 3 and assuming there is some residual hydraulic pressure to the flaps, does the system also require electrical power to lower the flaps and would the AC and DC ESS busses provide this supply?

As the pictures show, the flaps are clearly (partially) extended. Was this the result of remaining in a take off configuration, or extended subsequently ?

Configuration
 

Take into account noise abatement profile: reduce thrust passing 1500 ft and start cleanup passing 3000 ft.

Take into account the relatively short runways of La Guardia: optimum take-off configuration may well have been CONF 3, which is also an approved landing configuration.

Depending on the altitude at which the (dual) engine failure occurred, configuration on touchdown may well have been the T/O configuration and may have been the ideal configuration as well for ditching.

Starting APU: yes please, if the time was available for that.

Windmill RPM: 15 % N2 might give a useable amount of hydraulic pressure thruogh the engine driven pumps of blue and green systems. Have no idea though whether engine (damage) condition and airspeed would provide even that low amount of RPM.

With regards to RAT: for sure it provides pressure to flight controls (elevator, ailerons and rudder) but cannot say from the top of my head whether it powers slats and hydraulic driven generator.

Side note: pax, as usual, at least in my media, reported engine on fire: more likely the combustion flame peeping out of both ends of the engine as a result of an engine stall due to compressor and/or turbine damage.

Looking forward to investigation results but, for now, ditching performed in an examplary manner.

APU start considerations didn't really apply in this situation as they were so low at the time and visual with the surrounding, so I would of (if I had thought of it) started the APU. The problem comes when you are at cruising altitude with a double engine failure, getting the APU up and running ASAP is advantageous as it will allow you to keep the ADIRU's (within 7 minutes of GEN failure) up and running to give you route/airport info, will also allow some restoration of hyd and electrical systems. The problem will come if for some reason the APU doesn't start and you end up wasting most of your precious BAT time because at stated above when the airspeed gets to around 140kts the RAT will potentially failue leaving you purely on BAT power, this could be quite akward if at this stage you are not visual with the runway/landing site and you lose ALL instrumentation whilst IMC. Having said all of that I think that I would always have one go at an APU start (as recommended by the QRH) as you would have to be having a really bad day (again!!) for all the other stuff to go wrong as well. It is just important to understand the consequences of failed APU start attempts.

I agree with the above.
The advantages of an immediate APU start do by far outweigh the slight probability of your batteries going dead on short final in IMC. This usually is the first command even outside the checklist when in the sim with an engine failure (or two, sometimes...). Get back redundacy, and if both have failed, restore as many systems as possible to normal ops to avoid heavier workload. With the press of two buttons you have very good chances to get back pressurisation (not an issue at the Hudson, of course), and enough elec to run the hydraulic pump(s) and get CM2 his instruments back.

Nic

The books advise to not start the APU because if it is unsuccessful, you will have severley limited your time available on batteries only.

Even though the engines may have been damaged and flamed out, if the core is still rotating, the hyd pumps may have been producing some pressure. If we paratice a single engine landing in our 320 sim, the hyd pressure for the windmilling engine drops to the ECAM trigger on approach. Wheras, my colleagues who have done it for real say that the windmilling engine will produce sufficient pressure down to about 70 knots.

Windmill Start and APU....
 

The best speed for windmill start for the CFMs is 300 KIAS....and 280 KIAS for the V-2500s. Once you get slowed up toward green dot, the only hope you have for an in-flight start is to use the APU. (I suppose it's possible to do an air start at green dot.....just not likely.)

If you're going to start the APU, you must wait about 45 seconds after the RAT deployment (if my memory serves me correctly), to ensure the RAT is up and on line. Starting the APU while the Rat is starting to do its thing may screw up the RAT coming on line. (All this is on the paper checklist.)

Yes, attempting to start the APU will deplete the battery power, but the issue is not electrical....it's powerplant. You want to get at least one engine started. If you don't have enought altitude to push the nose over to get sufficient speed for an airstart, you have no choice but to use starter assist.


Fly Safe,

PantLoad

@ wileydog3: of course it is possible that the APU was running. Aircraft was heavy (150 pax) and it was cold. So it makes sense to perform the takeoff with packs on APU for performance reasons. In this case you still have the packs running for passenger comfort and you can increase your flex temp.

150 pax - not quite heavy, also applicable w/rgds to sector length.
cold - good for performance, time delay between RWY lineup and re-selecting a pack is irrelevant with regards of cabin cooling to affect comfort
flex increase - good for money saving, should you decide to keep APU on the fuel consumption offsets the savings.

I see no reason why would they need to keep APU on for departure, certainly not in based on the above. Let's wait for the report.

FD (the un-real)

not for fuel saving but for increasing flex temp to reduce the possibility of an engine failure. also reducing maintenance costs. packs on apu or off increases flex temp around 3 degrees. I don´t know how long the rwy is but I allways try to have a flex of 40 or more. Off course you can also switch the packs off without apu running but packs on increases cabin ventilation in addition to the cabin fans which are anyways too loud in the flight deck.
Edit: Just checked rwy length and calculated performance: rwy around 2100 meters long gives me following data for an A320 ZFW around 58000 and 8 tons of fuel for a two hours flight, wind calm: 134, 134, 137 with config 2 and flex 36.
So packs off or on APU is a good idea in my opinion.