Thrust Reverser Effects On Touchdown

[mirkoni]

Hi All,

I read in Park's notes for A320:

"Be careful not to let the nose ride up when reverse is selected. Select Full Reverse as you lower nose."

Why would this happen when the moment of opposite thrust force ("braking" force on the engines) would naturally pitch down the nose (aircraft CG is above the line of thrust)?

Maybe because of the combined effect of spoilers on touchdown? Effect of angled reverse jet flow?

OR, because choosing reverser first on IDLE during touchdown doesn't produce large reverse force, but cancels forward thrust, therefore suddenly unbalancing all of the moments around CG?

Both textbooks and FCOMs that I read state that reverser operation is possible already when main LGs are compressed. Why not wait for the nose gear because of these pitch moments?

[Goldenrivett]

Hi Mirkoni,
Be careful not to let the nose ride up when reverse is selected.
The turbulent airflow around the thrust reversers causes an increase in pressure under the wing. Since the engines are mounted inboard, the effect on a swept wing is to cause a mild nose up tendency. It is easily controlled by nose down elevators.

Why not wait for the nose gear because of these pitch moments?
Since it's not a problem to control, if you need Reverse thrust then take advantage of it early. Also wheel braking causes a nose down pitch, so just fly the nose wheel gently onto the runway.

[mirkoni]

Thanks Goldenrivet, for prompt and clear answer.

Do you happen to know if the reverser stow/deploy process on Airbus or Boing operation can be interrupted during the motor operation, or reverser has to stow or deploy fully in order to be deployed/stowed again? (i.e. in go-around situation, reverser started to deploy, pilot choses to go-around, can the pilot interrupt deployment to stowing immediately during sleeve movement)

[Goldenrivett]

Hi mirkoni,
i.e. in go-around situation, reverser started to deploy, pilot choses to go-around
It is not recommended.

When we were doing touch and goes during base training, if we ever selected reverse thrust accidentally, then it became a full stop landing. There are many reported incidents / accidents (Google search) where crews have attempted to GA after selecting reverse. e.g.

SKYbrary - A306, East Midlands UK, 2011 (LOC AW HF) (http://www.skybrary.aero/index.php/A306,_East_Midlands_UK,_2011_(LOC_AW_HF))

Reverse thrust deployment and why can't you take off again? [Archive] - PPRuNe Forums (http://www.pprune.org/archive/index.php/t-295464.html)

[stilton]

Once reverse thrust is selected the go-around option is no longer available.


That's straight out of my B757 / 67 flight manual and pretty standard Boeing procedure.

[sierra_mike]

i.e. in go-around situation, reverser started to deploy, pilot choses to go-around

the A320 FCOM/FCTM is pretty clear about that

After the flight crew selects reverse thrust, they must perform a full stop landing. (FCOM/PRO/NOR/SOP/Landing/LANDING)



In any case, if reverse thrust has been applied, a full stop landing must be completed. (FCTM/NO/NO 180-GO AROUND/REJECTED LANDING)


there is also an article about that topic available in issue 14 of Airbus' Safety First magazine