Low energy warning with thrust at idle A320

[hborderas]

Hi everybody I have a technical question.
On the A319: is it true that if you remain with A/THR in climb detent, and continue with IDLE on the PFD for a predetermined time you will receive a low energy warning?
if this is true how much time it needs to go by before you receive the warning.
Thanks

[TO MEMO]

Hi!

Not true!

That warning depends only on:
- aircraft config (2,3, and full)
- horizontal deceleration rate
- flight path angle

The warning will be repeated every 5 seconds and if no pilot response, will be followed by alpha floor protection (full power regardless of thust levers position).

[hborderas]

thnx TO MEMO

[IFLY_INDIGO]

can anyone give a practical scenario when this warning could activate during approach????

thanks in advance

[NVpilot]

Hand flown approach, base to final while tightening up the turn.

[IFixPlanes]

Quoting out of the AMM:

Low Energy Warning
General
The Low Energy Function is to prevent the A/C from entering a low energy situation by alerting the pilot through an audio warning:
"SPEED...SPEED...SPEED".

Pilot has to increase thrust and low energy warning disappears as soon as:
- Thrust level is high enough or
- Alpha floor protection is triggered or
- Pitch go around mode is triggered.

Low energy warning is available in configuration 2, 3 and FULL and between 100 ft and 2000 ft RA.
http://img509.imageshack.us/img509/8140/a320lowenergyqd7.th.jpg (http://img509.imageshack.us/my.php?image=a320lowenergyqd7.jpg)

Warning
http://img74.imageshack.us/img74/3474/a320lowenergy2mk7.th.jpg (http://img74.imageshack.us/my.php?image=a320lowenergy2mk7.jpg)
A combination of angle-of-attack, flight-path angle and deceleration is computed and compared to a threshold, depending on slat/flap configuration, typically 0.4 deg. to 1 deg. lower than alpha floor threshold.
When the result of the combination is above this threshold for more than 0.5 sec, low energy condition is triggered for at least 3 sec and sent to the FWC that elaborates the audio warning.

System aspects
The low energy detection is not duplicated.

[IFLY_INDIGO]

and presumably autothrust is off...
So is it a precursor to alpha floor protection?

thanx

[divinehover]

I have had a Low Energy warning on a A319 due to Windshear. Both A/P and A/T were engaged. The easiest thing to do is to advance the thrust levers beyong the climb detent to increase the available thrust (you will only have climb thrust avail when levers are inthe Climb Detent). The amount you increase will depend on how much power you require to get yourself out of the low energy situation.

Don't do what I did and go to TOGA (unless you need to) cause that opended a whole new can of worms.

[Dream Land]

No auto thrust does not need to be off.

[CONF iture]

Surprised by your anecdote divinehover, I thought a WINDSHEAR WARNING would prevail, and the procedure would be to apply TOGA.
Maybe it was not severe enough, or is that your aircraft was not equipped with a windshear detection system ?
I suppose it was landing phase (?)

[divinehover]

Landing phase (1400ft Conf Full). Windshear not detected (equipment fitted). FAJS ILS 03R.
Just because you've lost of few knots due to a bit of shear does it mean you need to do a G/A. Don't get me wrong. A G/A at any stage before rev deployment is a safe option if the situation calls for it. But if the situation can be rectified by advancing the thrust levers an inch, surely that's easier than a full G/A with another app in the same weather or a diversion. Once again. A G/A must be executed if the situation calls for it.

[TO MEMO]

As NVpilot said, the most common situation where you can get the warning is on base leg turning final while tightening the turn!

[FlightDetent]

As NVpilot said, the most common situation where you can get the warning is on base leg turning final while tightening the turn!
Especially when base-leg is into the wind and the HW component vanishes during the turn. If pilot manages to combine it with a hand flown level off during the turn out of the wind, the A/THR is late to respond (it did not see the level-off coming due to no ALT* with FDs off). Provided one had IDLE before the turn, I would consider the warning guaranteed. :E

FD (the un-real)

[TO MEMO]

You bet!

Usually the warning comes when you have idle before the turn...:p

[CONF iture]

Just because you've lost of few knots due to a bit of shear does it mean you need to do a G/A
Maybe not, but if you tell me that following a 3 deg downslope with CLB thrust was not sufficient to keep AOA away from 1 deg lower than alpha floor threshold (ref AMM a few post above), there is something more than "a few lost knots due to a bit of shear" ...

On the side, as you mentioned 1400 feet for that event, I can now see that windshear detection function is provided only below 1300 feet.

[Tail-take-off]

I too have had this warning but in a 321.

On a visual approach, autothrust active in speed mode, Flap 3 selected maintaining F speed. Turned onto finals (low TAS produced a good rate of turn) into a strong headwind & VAPP shot up by about 15kts due to G/S mini. VAPP now about 10kts above current speed resulting in "Speed Speed" warning & a huge increase in thrust.

Thanks G/s mini that helped a lot:D

[FlightDetent]

A321, idle thrust, F speed & F3 hand flown turn - those are the usual culprits. Just to make sure, the warning is by no way tied to undershoot the commanded speed. FCOM1 goes to say (my recollection) that is triggered when energy state is such that next pitch up command would not result in change of trajectory unless thrust is added.

As a bit of creep, does anybody know how is alpha max calculated? I suppose even on a FBW, it is not at aplha cy max, as any upset would put you on the downslope of aplha/cy.

FD (the un-real)

[divinehover]

This is a cut and paste from the FCOM. Doesn't really answer the question though.


Valpha PROT, Valpha MAX and VSW are computed by the FAC, based on aerodynamic data. They are only used for display on the PFD, and not for flight control protection (the activation of the protections is computed by the ELAC).

Valpha MAX : Maximum angle of attack speed.
Corresponds to the maximum angle of attack that may be reached in pitch normal law.
Represented by the top of a red strip along the PFD speed scale, in normal law.

[Bula]

Here's and easy way to avoid it.. mostly

Turning into a strong headwind on final select a speed higher then the anticipated G/S mini Vapp prior to managing the speed on final

[Joe Monsoon]

Just manage the SPD and let G/S min help you and do the job or A/THR off make sure that you keep eye on the wind and your ground speed add pit (power) speed so not get into low energy state :ok:

[IFLY_INDIGO]

therefore :

Low energy warning is an additional protection against dropping energy level and backs the ATHR (if on), works closer to ground while shooting approach..

cheers

[FlightDetent]

Low energy warning ....... backs the ATHR (if on), Not true.
Also, it has nothing to do with G/S mini, and flying managed SPD has nothing to offer when you turn out of headwind (that's when it is most likely to get low energy warning).

FD (the un-real)