TAP029: The NEO Part 1

30 May 2017 15:36

It's the NEO Trio (see what we did there!)

 

Engine starting.
This is the most common thing we do with them so seems like a good place to start.
The sequence is still the same but helpfully, Airbus have decided to change the names of the controls, so, the ENG MASTER switch’ is now called ‘ENG MASTER lever’
And the ‘ENG MODE selector’ is now called ‘ENG START selector’

So as you do with the CEO, you turn the ENG START selector to IGN/START and this brings up the engine system page and closes off the pack valve.

When the engine master Lever is set to 'on' the start sequence begins.

On the CEO, the sequence runs like this,
The LP fuel valve opens
Start valve is opened
APU speed is increased (if that's being used for start)
If starting in the ground, When N2> 16% ignitions starts. In the air it's immediate
On the ground, when N2> 22% the HP Fuel valve opens. In flight it's when N2> 15%
Once the N2 gets above 50% the start valve closes, the igniter goes off unless in the air, the APU speed reduces to normal speed and the pack valve remains closed for 30 seconds (which you will already know of course because we discussed that a few months ago in our air conditioning episode!)
So what does the LEAP engine do?
Well for a start (no pun intended), the FADEC will initiate ignition and fuel flow at an optimal point during the start process instead of at defined N2 values like the CEO.
The numbers stated in the FCOM are pretty much the same, >15% N2 for ignition start (immediately if airborne) and >20% N2 for the HP fuel valve to open both on the ground and in the air.

As you can see, the procedure is the same, turn the engine start selector to ignition and then move the desired engine master lever to on.

Now, after starting, we normally do the approximate check of the engine parameters saying 2,4,6 and 3 Representing N1 / EGT / N2 / FF are 20% / 400°C / 60% / 300kg/hr
On the NEO, the Basic check of idle parameters is slightly different. The middle two figures have increase by one so it's 2,5,7 and 3 representing N1 / EGT / N2 / FF are 20% / 500°C / 70% / 300kg/hr

The biggest difference with the start is a new function performed by FADEC called pre-start motoring or dry cranking. Depending on the thermal state of the engine, FADEC will dry crank for up to 60 seconds prior to initiation of the start sequence. This can happen on both automatic and manual starts. During this motoring, FADEC will limit the N2 to a maximum of about 30%.
Just for some additional, geeky, background information the reason for this is because After shutting down, the engine components cool at different rates because of natural convection, and this leads to varying thermal gradients across the shaft section of the engine which can cause vibration. So this cranking protects the engine, Airbus' term is Bow Rotor Protection by spinning the engine up getting airflow through it and makes the heat dissipate evenly throughout the hot section components prior to engine start.

Airbus have also changed some of the terminology around the engines idle states.
IDLE
What was 'modulated idle' on the CEO is now called ‘Minimum Idle’ on the NEO.
Approach Idle, which is a higher thrust setting than Minimum Idle to allow the engines to accelerate from Idle to TOGA thrust in the required regulatory time is now set when landing flap is selected (CONF 3 or FULL) or if the gear is selected down. For the CEO, Approach Idle is set when the flap lever is not in the zero position, basically with selection of Flap 1.

 

Max oil quantity is increased from 22QTS to 24.25QTS.
Minimum QTY increased from 9.5qt + 0.5qt/hour to 10.6qt + 0.45qt/hour.
Minimum oil temperature for start increased from -40°C to -29°C
Minimum oil temperature for take-off increased from -10°C to +19°C, so quite a difference there.

Starter limits are now as follows,
Starter:
Maximum number of start attempts reduced from four to three.
Pause between start attempts increased from 20s to 60s
Maximum running engagement of starter increased from 20% N2 to 59% N2

The EGT limits have changed and the amber and red bands reflect this. The operation is the same so we're not going to read off all these figures and they'll just get lost in our minds.

N1 Max has been reduced from 104% to 101% and N2 MAX has increased from 105% to 116.5%

The vibration displays have changed giving three options now, green, pulsing green and amber. The amber indication isn't available on the CEO. This also come with a new ECAM alert which triggers when the high vibration threshold is reached on N1 or N2. Crew are then directed to action the High Engine Vibration Checklist. The ECAM will say,
HI ENG VIB PROC...................................................................................................APPLY
Of course on the CEO you just get the advisory pulsing.

Next, wind limitations, yep, they've changed those too!
Wind limitation for starting: Max crosswind 45kts.
The crosswinds are different for take off and landing like they used to be with A max of 35kts for T.OFF and 38kts for Landing.
For automatic landing and roll-out:
Max Headwind 20kts
Max Tailwind 5kts
- Max Crosswind 15kts

Turbulence Penetration Speeds have been increased from 250kts to 260kts (below FL200) and from 275kts to 280kts (above FL200).

An Engine run-up is only required on the NEO if icing conditions exceed 60mins (it is 30mins on the CEO). After the 60 minutes, the engines should be increased to 70% for at least 5 seconds.
When operating in ground fog icing conditions, an engineering inspection should be performed on the engine if take-off not performed with 120mins

Something that's worth mentioning for those of you operating outside of Europe, the NEO has a restriction in the landing flap at high altitude airports. If the airport pressure altitude >2000ft, you have to use Flap 3 for approach if a minimum go around gradient of 4% can't be achieved. Theres a table in the FCOM-LIM section where you can check the restricting weight - most are well above MLW. This flap restriction will only occur below MLW at very high temperatures or very high pressure altitudes).

 

Probably the most noticeable difference for the crew is the automatic anti icing system. Within the engine, the NEO will automatically introduce hot air to the engine core when required to prevent ice crystal formation in the CORE of the engine, 'CORE ICE PROT’ is displayed on the ENG SD when it's active. It Also has a Booster Anti-Ice for prevention of ice in the booster section of the engine (‘BOOST ICE PROT’ is indicated on ENG SD Page when it's active. Remember though, these new features are only for internal anti-icing and don't remove the requirements for us to use engine anti ice

Another feature that's been added is protection against uncontrolled high thrust during critical phases of flight. This is called Thrust Control Malfunction Accommodation (TCMA) and is active on the ground and during takeoff and the approach phase. The TCMA protection logic will reduce fuel flow in flight or shutoff fuel on the ground, whenever an over-thrust condition is detected.
There's also something called a Transient Bleed Valve (TBV) which reduces the risk of engine stall during acceleration or deceleration of the engine.

There are some new memos which appear on the E/WD which are only available when the thrust levers are in TOGA or FLX/MCT detent. They are all displaying in a line above the N1 gauges.
With PACK pb-sw selected ON, 'PACKS' (MEMO)
When WAI is selected ON, 'WAI' (MEMO)
When EAI is selected ON, 'NAI' (MEMO)

FADEC has some new features too.
Transmission of vibration information to cockpit indicators
Protection against engine stall and engine flame-out
Thrust Control Malfunction Accommodation
Protection against bowed rotor during engine start on ground
Terminology difference: The CEO FADEC is also referred to as the ECU (Engine Control
Unit). The NEO FADEC is referred to as the EEC (Electronic Engine Control).

 

 

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Duration: 20:59


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