Engine spool up on approach - Airbus

[jaja]

Most airlines have engine spool up as a criteria for a stable approach, e.g. engine spool up at a certain altitude, for example 1000'

Normally this is considered as engine being above idle when passing the above altitude.

The Airbus has an Approach idle mode.

I have just heard that being at Approach idle is sufficient, you do not need to have engine spool up.

Is that correct ?

[TopBunk]

No!

Approach idle, iirc, is automatically set when airborne when the flaps are extended so as to improve the engine response time to the standard required by the authorities.

It is higher than ground idle, but it still idle power.

The engines should approximately be at final approach setting at the gate altitude. Obviously it is not an exact science as the atmosphere is not uniform, but the thrust should be above idle.

[FlyingStone]

The only reason aircraft have approach idle (or high idle or whatever it's called) is to meet the 8 second certification requirement. It could obviously not be achieved from a normal (ground) idle, so higher idle setting is introduced so to achieve full rated thrust in 8 seconds.

Stabilization criteria is up to the company, as long as it is acceptable to the relevant authority. Some Airbus operators indeed have SOP where you can be stabilized with idle thrust, as long as other parameters are within limits.

[eckhard]

Stable Approach Policy criteria (inter alia) of an EASA-certified airline that operates Airbus and Boeing:

...........

An approach is considered stable when all of the following criteria are met:

In the planned landing configuration........

Stabilised on the correct vertical profile........

Stabilised at the target approach speed (taking into account the prevailing conditions – see Note).........

...........

The 'note' has words to the effect that, exceptionally, the speed may be above the target at 1000ft provided that it is reducing and that the crew are confident that it will be at the target value by 500ft. If this is not achieved, a go-around will be flown.

So, although there is no mention of engine thrust/power/rpm/EPR, it is implied that the engines may be at idle at 1000ft while the speed reduces to the target. If the target speed is achieved by 500ft, the engines will be spooling up to maintain the speed; however, there is no explicit requirement to check that this is so.

[jaja]

Thank you gentlemen for your answers

Airbus do not mention anything about engine spool up, so please confirm that Approach idle is sufficient all the way to retard ?

And that a requirement for engine spool up, is a company requirement and not a requirement as pr Airbus SOP ?

Are there any references you can refer to ?

[flyingchanges]

Pretty sure go around from idle is not a certified or demonstrated maneuver.

[tdracer]

Pretty sure go around from idle is not a certified or demonstrated maneuver.

Careful, go-around from minimum flight idle is not a cert requirement but 8 seconds from 'approach idle' (or whatever idle you get with the aircraft in a normal landing configuration) is a cert requirement and is most definitely demonstrated during cert.

As others have noted, with the flaps in landing the thrust needed to maintain airspeed is well above approach idle. We had a FADEC s/w error on a Boeing installations ~20 years ago that resulted in "approach" idle not being selected with the flaps in landing - the scary part was that apparently this error existed for over a year before anyone noticed because the thrust required with landing flaps was so much higher than idle.:eek:

[underfire]

Isnt the spool up just before the MDA/DA?

[Gysbreght]

Reader tdracer is correct. The certification performance requirement (current version) is:
Sec. 25.119

Landing climb: All-engines-operating.

In the landing configuration, the steady gradient of climb may not be less than 3.2 percent, with the engines at the power or thrust that is available 8 seconds after initiation of movement of the power or thrust controls from the minimum flight idle to the go-around power or thrust setting--

[flyingchanges]

ASN Aircraft accident Canadair CL-600-2B19 Regional Jet CRJ-100ER C-FSKI Fredericton Airport, NB (YFC) (http://aviation-safety.net/database/record.php?id=19971216-0)


The conditions under which the go-arounds are demonstrated for aircraft certification do not form part of the documentation that leads to aircraft limitations or boundaries for the go-around procedure; this contributed to these factors not being taken into account when the go-around procedures were incorporated in aircraft and training manuals.

- The published go-around procedure does not adequately reflect that once power is reduced to idle for landing, a go-around will probably not be completed without the aircraft contacting the runway (primarily because of the time required for the engines to spool up to go-around thrust).

Text above is quoted from the link.

I don't have the article (might have even been the ALPA magazine), but I distinctly remember the part about go around from idle not being demonstrated.

[tdracer]

I don't know what Canadair did, but it's specified in the regulations and I know for a fact that every Boeing jet aircraft had to demonstrate it met the 8 second requirement from approach idle during the certification flight testing. If Canadair really failed to meet the regulation, I think a major lawsuit would have put them out of business. It's certainly true that below some altitude a go-around is likely to result in ground contact (8 seconds can be a long time - ask the A320 pilot at Habsheim) but achieving go-around thrust in 8 seconds is a firm cert requirement.

I believe FADEC has done away with this, but for the 747 with the older hydromechanical controlled engines there is (or at least was) an MPD task where you needed to test the go-around accel characteristics - I think the interval was something like C-check.

[FlightDetent]

Airbus do not mention anything about engine spool up, so please confirm that Approach idle is sufficient all the way to retard ?

And that a requirement for engine spool up, is a company requirement and not a requirement as pr Airbus SOP ?

Are there any references you can refer to ?
a) No, absolutely it is not.

b) Not exactly. Airbus ask you to be at landing flap with Vapp on a 3 deg profile at 1000 ft. [FCTM NO-APPROACH GENERAL: The decelerated approach] This is not possible with engine idle, as you well know. The N1 setting are available from PEP, OCTOPUS or unreliable airspeed checklist. (*) 52 n1 is a good figure.

c) Yes; plenty more that'd we like. Reference 1. (http://www.ntsb.gov/news/events/Pages/2014_Asiana_BMG-Abstract.aspx) Reference 2. (http://aviation-safety.net/database/record.php?id=20090225-0) Reference 3. (http://lessonslearned.faa.gov/ll_main.cfm?TabID=1&LLID=71) Reference 4. (https://en.wikipedia.org/wiki/Air_France_Flight_296)

regards,
FD.

(*) I'd be happy to discuss if we could second guess AIB reasons not to quote a figure for N1 - LATER. :cool:

[underfire]

Landing climb: All-engines-operating.

In the landing configuration, the steady gradient of climb may not be less than 3.2 percent, with the engines at the power or thrust that is available 8 seconds after initiation of movement of the power or thrust controls from the minimum flight idle to the go-around power or thrust setting--

So, engines should be spooled up 8 seconds before minimum (not a fixed 1000' or any fixed altitude, but using the minimum) to insure GA power without violating MDA/DA.

[BizJetJock]

Canadair/Bombardier aircraft definitely demonstrate meeting the same requirement. Flying it as a test point is quite fun, done at a reasonable altitude.
The point in the report applies to any aircraft; once you have pulled the thrust levers back to idle in the flare, you are extremely unlikely to be able to hold the aircraft off the ground for the time it takes for the engines to spool up again.
While you do not need full GA thrust to hold the aircraft level in ground effect, the acceleration is not linear. For about 4-5 seconds there is often (depending on engine type) very little increase in thrust, then it all comes at the end. Which is another part of the equation for the stable approach having more than idle thrust, since it reduces to time to GA hugely.

[vilas]

EMIRATES – STABLE APPROACH CRITERIA
Stable Approach Criteria
An approach is considered to be stable when all of the following conditions are met:
All briefings and checklists have been actioned.
The aircraft is in the planned landing configuration (Note 1).
The aircraft is on the correct flight path (Note 2).
The aircraft speed is not more than final approach speed +10 KIAS and not less than
VREF (Note 3).
Power setting is appropriate for the aircraft configuration.
Note 1: Planned landing configuration is: landing gear down and locked, landing flap set and speedbrake armed.
Note 2: An aircraft is considered to be on the correct flight path if it is within the approach path laid down in the fleet specific FCOM.
Note 3: As adjusted by minimum ground speed techniques where applicable and excluding momentary excursions (a momentary excursion is defined as a deviation lasting only a few seconds and where every indication is that it will return within the stabilised criteria).

[jaja]

Thank you for all the answers, but it still has not answered ny question.

Airbus SOP requires a "Stabilized" call at 1000'. To be stabilized according to Airbus SOP requires the following :

The purpose of this call is to ensure both pilots are aware of the aircraft energy status/configuration and force a decision if the stability requirements are not achieved by this point.

The required paramenters are found in the SOP under "Flight Parameters in Approach"

So my question is : if you under certain conditions fullfill all the above, BUT only have Approach Idle (no engine spool up) at 1000', and/or all the way to touchdown, is that OK according to Airbus SOP ?

[Capn Bloggs]

BUT only have Approach Idle (no engine spool up) at 1000', and/or all the way to touchdown, is that OK according to Airbus SOP ?
That is an impossibility. If you're on-speed at 1000ft ie Stable, there is no way in the world you'll still be on-speed with the power still at Approach Idle (or whatever you want to call it) or conversely, there is no way that you can't be well above approach idle if you're still on-speed later on. This is so basic that I very much doubt Airbus would even consider mentioning it.

Most airlines have engine spool up as a criteria for a stable approach, e.g. engine spool up at a certain altitude, for example 1000'
"Most airlines"? Would you mind giving some example text (obviously stating aircraft type).

"Spun up to bleed valve closure". Those were the real days...

[Chesty Morgan]

Power setting appropriate for configuration is a nonsense statement invented by lawyers.

[ElitePilot]

I think the "power appropriate for configuration" does answer the question.
If you're Conf3, 9kts above Vapp at 1200' and you got an increasing tailwind/reducing headwind (GS mini reducing) while rather heavy, autothrust will give approach idle or close to.

Stable? Or around from 1000'?

[Capn Bloggs]

Stable. You will not maintain that situation (eg increasing tailwind) for more than a few seconds. If you do, then Go Around.

[RAT 5]

Power is there to maintain a speed no matter what the configuration. As has been said the atmosphere is not a static entity. It is changing and so therefore will the power setting necessary to maintain the speed. Due to short lived shear factors the power could be quite variable for a few seconds. It is not uncommon to give a significant burst followed almost immediately by a reduction to datum; or equally a handful reduction and then back to datum.
It would be sod's law that this happens at landing gate and you have an overly keen PM with the SOP call of "continue" or "Go-around" and they close the latter.

[FlightDetent]

Thank you for all the answers, but it still has not answered my question. As we failed to convince you, here's one from non-modified Airbus A320 FCOM, that hopefully will help solve your dispute:

...
In order to be stabilized, all of the following conditions must be verified before, or at this stabilization height:
‐ The aircraft is on the correct lateral and vertical flight path
‐ The aircraft is in the desired landing configuration
‐ The thrust is stabilized, usually above idle, in order to maintain the target approach speed along the desired final approach path
‐ There is no excessive flight parameter deviation.

[oicur12.again]

"Usually above idle" is vague and does not clearly solve the riddle.

as long as you hit the stable point as required by the company, then you will probably be powered up. Although sometimes a lightly loaded 330 on a gusty day will hit the idle stops occasionally all the way down final.

approach idle is designed to eliminate the need for a specific spool up setting on final which is why its vague and no setting is published.