Airbus Driver Question:

[Louie1975]

So as a fairly new Airbus 320 FO, I have a question that is stumping me. It's also my first Autothrust or even autothrottle airplane.

A manual I have says something to this effect. 'The FADEC computes the thrust rating limit for each thrust lever position. If the Thrust Lever is set in a detent, the FADEC selects the rating limit corresponding to this detent. If the thrust lever is set in between two detents, the FADEC selects the rating limit corresponding to the higher detent'.

But then in another manual titled 'Airbus A320: An Advanced Systems Guide', it says this...'When the Thrust Levers are set between two detents, the limit value displayed is based on the upper detent, but the actual value corresponds to the ACTUAL POSITION(my emphasis) of the thrust levers'.

So my question is this...when you are landing with Autothrust engaged, in the flare, (and get the corresponding RETARD aural alert), you then pull the thrust levers out of Climb detent and into Idle detent(disconnecting auto thrust). When is the actual EPR of the engines being reduced to idle? According to the first manual I referenced above, it won't be until you are in Idle detent. In Other Words, you are doing nothing in between the two detents, until you get to Idle. According to the way I am reading the second manual I quoted, it will be when the Thrust Lever Angle matches the actual EPR, because the Thrust Lever is acting as a Thrust Limiter. So in this scenario, you are actually doing something in between the two detents, because the rate of EPR decrease will be directly proportional to the rate you bring the Thrust Levers back(of course once your Thrust Lever Angles match actual EPR).

Hope my question is clear. Practically speaking its not really a big issue on landing, since EPR is probably almost Idle anyway. But this is just to enhance my understanding.

 

[BobDDuck]

The thrust will decrease as you pull the levers back. Upon reaching the idle detent the thrust will be (limited to) idle.

What the first source is saying is that the LIMIT (not the actual thrust number) will be for the detent you are in OR if you aren't in a detent, the detent above where you currently are.

 

[Skåning]

I'm an Airbus noob too and if I remember correctly from systems, autothrust is active only from the climb detent to just above idle. So I believe the engine doesn't reduce to idle until you actually hit that idle detent. Same as when you're in another phase of flight.

 

[Cherokee_Cruiser]

On approach with AT on, assuming flaps full, the N1 is about 45-55% depending on a headwind/tailwind situation. The levers are in the CLB detent is the normal position. As you pull the thrust levers back, the donut is the new thrust limiter. Assuming you pulled early and slow, it would flash lever climb in any other regime of flight. But in the case of landing as you pull the thrust back the corresponding donut is the thrust limiter , and it goes to idle as you progressively pull the thrust lever back. The actual idle amount is just before the physical idle position.

We got a nasty gram a while ago about a certain technique that was observed on the line in windy conditions. Because the AT sometimes fluctuates depending on how windy it is, some guys were approaching with AT on, but thrust lever pulled back to about 55-60% N1 to make sure it wouldn't go above while fighting winds. Standards response was that AT should either be on or off, and that if a pilot wants to limit the thrust in any way, do it manually with AT off.

 

[Toobdrvr]

Bob and Cruiser nailed it.

In a perfect world, the difference between CL and Idle on landing would be approach thrust- ground idle. When you pull the TLs back, you're reducing the upper limit from approach thrust-ground idle.

 

[Louie1975]

Thank you guys. That explained it for me. I appreciate these responses! What a different airplane than anything I've ever flown before!!

 

[woodreau]

Thank you guys. That explained it for me. I appreciate these responses! What a different airplane than anything I've ever flown before!!

Just wait until you're in managed descent and Fifi get's confused....

On a different note, these NEO engines appear to be a pain in the butt, we are going thru differences training and the thing that jumps out at me is engine start.

Flip the engine master to ON, on a normal engine, FADEC initiates the engine start sequence. For the NEO, it figures out whether the engine needs a cooldown before start, so instead you get a "COOLING" message with a 2:00 minute counter which counts down as the engine dry motors. After it reaches 0, it initiates the engine start sequence. Then 5 minutes after engine start for warm up before you can apply takeoff power.... Looks like no more single engine taxi for this bird.

 

[BobDDuck]

On a different note, these NEO engines appear to be a pain in the butt, we are going thru differences training and the thing that jumps out at me is engine start.

Flip the engine master to ON, on a normal engine, FADEC initiates the engine start sequence. For the NEO, it figures out whether the engine needs a cooldown before start, so instead you get a "COOLING" message with a 2:00 minute counter which counts down as the engine dry motors. After it reaches 0, it initiates the engine start sequence. Then 5 minutes after engine start for warm up before you can apply takeoff power.... Looks like no more single engine taxi for this bird.

Is this with the P&W engine? If so, my understanding is that this is a temporary fix to fan blade issues and will probably be solved in the future. This was why several carriers that had early order number slots refused the airplane until the engines weren't so restricted.

 

[woodreau]

On approach with AT on, assuming flaps full, the N1 is about 45-55% depending on a headwind/tailwind situation. The levers are in the CLB detent is the normal position.

Are your Airbuses normally controlled with N1 or EPR? Just curious if this was a engine type specific thing like CFM vs IAE.

Is this with the P&W engine? If so, my understanding is that this is a temporary fix to fan blade issues and will probably be solved in the future. This was why several carriers that had early order number slots refused the airplane until the engines weren't so restricted.

I believe it is with the P&W engines... This is the procedure that is being sent out in our training materials, whether it's a temporary thing or not I have no idea.
We've got several airplanes deferred sitting around waiting for engines, but I guess we will finally get the first one in September... Whether it will actually arrive or not who knows? We'll see how much of a hangar queen it is. I hear Lufthansa has been flying their one NEO on sectors back and forth between their three maintenance bases - rumor is that it can't fly into high and hot (well it will get in, whether it will fly out is another matter), i.e. LAS so I don't know what it's capable or not capable of.

 

[Skåning]

Are your Airbuses normally controlled with N1 or EPR? Just curious if this was a engine type specific thing like CFM vs IAE

N1 on the CFMs

 

[Cherokee_Cruiser]

Are your Airbuses normally controlled with N1 or EPR? Just curious if this was a engine type specific thing like CFM vs IAE.



I believe it is with the P&W engines... This is the procedure that is being sent out in our training materials, whether it's a temporary thing or not I have no idea.
We've got several airplanes deferred sitting around waiting for engines, but I guess we will finally get the first one in September... Whether it will actually arrive or not who knows? We'll see how much of a hangar queen it is. I hear Lufthansa has been flying their one NEO on sectors back and forth between their three maintenance bases - rumor is that it can't fly into high and hot (well it will get in, whether it will fly out is another matter), i.e. LAS so I don't know what it's capable or not capable of.

N1 for CFM engines, there is no EPR gauge. N1, EGT, and N2.

 

[Cptnchia]

N1 for CFM engines, there is no EPR gauge. N1, EGT, and N2.

Everyone uses N1 except P&W. If they built a lawnmower engine, it'd have an EPR gauge on it.

 

[BobDDuck]

Everyone uses N1 except P&W. If they built a lawnmower engine, it'd have an EPR gauge on it.

After flying a plane with EPR for over 3 years now, I still never look at the thing and use N1 to set thrust for everything except confirming takeoff power.

 

[Cptnchia]

After flying a plane with EPR for over 3 years now, I still never look at the thing and use N1 to set thrust for everything except confirming takeoff power.

EPR is for auto throttles, N1 is for pilots.

 

[OneNineHundy]

I've just switched from flying Boeings the past 5 years (733, 738, 787). Now doing my Airbus course I have to say how much I enjoy the plane over the old 73's. Much larger cockpit, and seems light-years ahead of the 73. Some things even seem more advance than the 787.

Sent from my SM-N920I using Tapatalk

 

[Autothrust Blue]

Do NOT neglect setting the thrust levers to idle.

(That sounds elementary, but I only say so because someone tried it and are no longer around to brag about it. https://en.m.wikipedia.org/wiki/TAM_Airlines_Flight_3054 )

 

[Roger Roger]

Do NOT neglect setting the thrust levers to idle.

(That sounds elementary, but I only say so because someone tried it and are no longer around to brag about it. https://en.m.wikipedia.org/wiki/TAM_Airlines_Flight_3054 )

On the one hand, people need to be pilot. On the other, human interfaces and intuitiveness.

 

[Autothrust Blue]

On the one hand, people need to be pilot. On the other, human interfaces and intuitiveness.

I studied the Airbus flight control system quite a bit in software classes in college. I'm less than enthused, to be honest, from a human-computer interaction standpoint. It's cool and all, but it's a great demonstration of what happens when you try to idiot-proof something: the universe constructs better idiots.

 

[nimslow]

EPR is for auto throttles, N1 is for pilots.

I don't think I've ever flown with anyone on the -80 that uses N1 to set power normally, just about everyone uses EPR as the primary power instrument when manually working the throttles (or when constantly "helping" the auto throttles).

I start the formal Airbus school the end of this month, but I just finished the required 20+ hours of systems home study. I'm going into it with an open mind, but I can't say I'm a fan of the way they do things.

 

[Cptnchia]

I don't think I've ever flown with anyone on the -80 that uses N1 to set power normally, just about everyone uses EPR as the primary power instrument when manually working the throttles (or when constantly "helping" the auto throttles).

While this is true, you don't just blindly set power by EPR. You need to cross check your N1 to ensure you don't have a faulty probe. You can trash an engine doing that. Low faulty EPR, you push the power up to match EPR, now you just exceeded N1.

Or conversely, the Air Florida crash. Had they looked at their N1 instead of just the EPR, they would have noticed the low power output of the motors.

"Following the lengthy investigation into the Potomac accident, notices were sent to all operators of Pratt & Whitney JT8D series engines, warning that crews should be on alert for erroneous EPR indications in icing conditions and to rely primarily on the engine RPM gauge for actual indications of power. Typically, the RPM gauge is called an N1 or Fan gauge and will usually show 35% N1 while idling, 83% in cruise, and 95% — 101% on takeoff. Blocking of PT2 tubes by substances other than ice was not discussed in the Alert Bulletin."

It's basic pilot stuff.