Airbus: Power to Idle at 50' or 30' or elsewise?

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Airbus: Power to Idle at 50' or 30' or elsewise?

Post by News&Safety » July 11th, 2019, 1:49 am

There are many opinions. They fact remains.. it depends. Ultimately, it isn't one simple answer. We tend to agree with contributor #4.

From airbusdriver.net:

Contributor 1:
* Our pilots handbook does NOT say to retard at 50 feet, contrary to popular belief. It clearly says over the runway threshold. (which is "about" 50 feet when on the proper glidepath).

* Retarding at 50' in Denver on a hot day will result in the aluminum tube descending to impact planet earth at a higher vertical velocity than most passengers are comfortable with. Trust me. Something to do with less lifties in the air over Colorado.

* An Airbus test pilot recently said that we should NOT retard at the 50 foot callout. They are trained by Airbus Industrie to retard at the RETARD callout. (Duh)

* The 50 foot auto callout sometimes is not called out. Or the 100. Or the 1000. These are all good reasons NOT to get into a serious habit of relying on a synthetic voice to do things like retard the thrust levers.

* The N1's at 50 feet are near idle normally, so that the retarding is more or less a matching of levers with condition, and does not "really" do a whole lot in terms of thrust application.

* Technique: When I retard, I don't slam them to the stop, but I do bring them back to the stop with enough momentum to HEAR the stop being contacted, which in a subtle manner tells the non-flying pilot that I have retarded the levers.

* Retarding prior to 50' is ugly, particularly if you hold off for a smooth touchdown, since Alpha Protection is soon on its way.

Contributor 2:

Pulling the thrust levers off at 50 ft accomplishes two important functions. First, if you leave the thrust levers in the climb detent and get slow during the round out and flare, the power will come in to compensate just when you are trying to land!!! This, of course, extends your landing distance which could be critical at certain airports and runway conditions. The system acts this way because you are in the "speed" mode at 50 ft and the speed selected on the FCU is what the computer will try to maintain until you disconnect the Autothrust. Second, the thrust levers MUST be at idle during touch down or you will not get the spoilers to deploy after landing ... also extending your landing roll distance. So the golden rule is that you must be at idle on touchdown.

Having said the above, lets add real world factors and discuss "being the pilot." We have all experienced running out of airspeed prematurely when we robotically pull the levers at 50 ft., especially if you have flared high. This is where being the pilot comes in. If your approach speed (Vapp - magenta triangle) is ref plus 5 (as it most always is) you have only that small margin of speed to accomplish round out and flare. There are times ground speed mini will give you more than ref plus 5. There are times when YOU will modify Vapp to compensate for gusty winds, icing, suspected windshear, or an ECAM procedure. So, as you would in any aircraft, pull the levers to idle when it is appropriate. What exactly is appropriate?? With excess airspeed over 5 kts and normal landing conditions, pulling the levers all the way to idle at 50 ft will work well. When conditions give you ref plus 5 or on rare occasion, less, then it makes sense to delay thrust reduction to the idle detent until approximately 30 ft.

Here is where understanding the system comes in. Under routine operation, at 50 ft the engines are already at idle. If you were to pull the levers out of the climb detent at this time and bring the levers to 12 o'clock (straight up on the quadrant) you have done NOTHING to your current thrust condition. What you have done is gone into the active range and reset the upper limit of what the FADEC will give you. At 30 ft you continue to idle and bleed off the rest of the thrust and disconnect the Autothrust system preventing a power addition if you get slow (you want to get slow!!) This seems to work well with the 321 as well.

If you have pulled the thrust levers to idle but have found yourself high in the flare, remember that you now have manual thrust and it may behoove you to push the levers forward to get some airspeed back to arrest your sink rate.

Contributor 3:

TO IDLE, OR NOT TO IDLE, THAT IS THE QUESTION


The PH states on page 18-67, "To land in this range, the thrust levers must be brought to idle upon crossing the threshold (this is 50’ with CONF FULL). Do not attempt to touchdown with the thrust levers above idle." This statement is based on perfect conditions, standard day, calm winds, at sea level. How many of those have we ever had? Chapters 4 thru 17 in the PH are how the systems work and operate. Chapters 3 and 18 are how we, as pilots, work and operate the systems.

There is nothing magical or mechanical about 50’. It is an airplane. The "philosophy" of landing an airbus is the same as any other airplane. Every landing is different, always has been and always will be. Fifty feet is to be used for guidance. During an autoland approach the aircraft begins to reduce thrust just above 20’ and the F/O is to “verify thrust at idle” at 20’ (PH 18-47). Put the airplane at Denver on a hot day, an altimeter at 30.10 with gusty winds and watch what happens. What makes this airplane different is the thrust levers are in a detent during flight until just prior to touchdown. The climb detent is considerably higher than the actual thrust setting (87% vs. 52%). If you begin to retard the thrust levers at “approximately” 50’, you will begin to match thrust levers and thrust between 30’ and 20’ also.

The consensuses of people with a lot of time on the airplane, line pilot and check airmen, is not to mechanically pull, or snatch the thrust levers to idle at 50’. Many factors help determine when to reduce thrust: wind, altitude, length of runway, contamination, speed, ref plus, weight of the aircraft, etc. Sometimes you begin to retard the thrust levers at 70’, sometimes at 50’, sometimes at 30’, and sometimes at 5’. Do make sure the thrust levers are at idle at touchdown so the spoilers will deploy immediately. Even during an autoland where the thrust moves to idle with the thrust levers still in the climb detent, the spoilers will not deploy until “----both thrust levers are at idle (if the ground spoilers are ARMED),…” (PH 12-4).

The problem is pilots are too mechanical, refuse because it is perceived as different than everything else they have ever flown, move the thrust levers much too quickly, move the thrust levers much too slowly, doesn’t make sense, etc. If you understand the TL system and realize 50’ is a start point, it will help prevent long, floating, nose high, ref minus landings…and maybe even a tail strike.



Contributor 4:

A good and totally "unofficial" technique for retarding the thrust levers to idle during the landing flare is to begin to retard the thrust levers at 50 feet for the 319, 40 feet for the 320 and 30 feet for the 321. Obviously there will always be additional circumstances to consider (wind, temp, weight, field elevation, etc.), but this is a terrific starting point that works well for the majority of situations and will put you in the ball park. This technique will help to prevent long floats on short runways or planting a heavy airplane on a hot day. Just remember 50-40-30 for the 319-320-321!

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