A321 - vibration on rotation

[skyshadow]

I recently travelled to Tenerife on an A321-211.

Both outbound and inbound the aircraft on rotation proceeded to vibrate severely prior to the main gear leaving the runway. I've never experienced this before on this type of a/c (I've flown on the actual plane twice before). Can anybody explain the likely cause of the vibration (it was shaking the whole plane including the overhead lockers).

MTIA.

[tom775257]

The nose wheels being out of balance I would think. Certainly I can feel it quite often on the A320 when the nose wheel is at speed (not severe vibration though certainly!)

Regards, Tom.

[Capt Fathom]

Nose Wheel Shimmy!
Caused by:
Uneven tyre wear. Uneven tyre pressures. High groundspeed due to heavy weight take-off, incorrect pressure in the nose wheel oleo!
Feels and sounds awful, but is not uncommon!

[skyshadow]

Thanks Tom & Captain,

Perhaps severe would be overstating it, but it was enough to cause a stir and make folks look a tad worried.

Cheers.

[matthewgamm]

A bit off-topic...

Just curious, what are the acceptable engine vibration levels on the ground, prior to take-off, and in the air?

My guess is, it is something like 5.1 in the air and in the vicinity of 6 on ground.

Thanks

[tom775257]

According to my QRH (CFM-56s).

There is an ECAM advisory when N1 vibration is equal or greater than 6 units, or N2 is equal to or greater than 4.3 units.

It states: the (advisory) is mainly a guide to induce the crew to monitor engine parameters more closely.

The procedure states if there is a rapid increase in vibration above the advisory, retard the affected engine's thrust lever.

On ground I would suspect icing, and a run up to 70% N1 should shed the ice. In flight if there is icing induced vibration, the engine can run up to shed ice, in idle descent for example.

Sorry I don't have FCOM 3 to hand to elaborate further.

[perkin]

I've noticed 737's always seem to have a little shake just as they get airborne...is it the same effect? (l/gear induced as opposed to engine vibration)

[Rainboe]

Well you would shake a little bit if your oleos suddenly violently extended to their stops, and your main wheels were rotating at a circumferal speed of about 160 kts and slightly out of balance before the brakes were applied!

[Dream Land]

Flew one two days ago that had this written in the tech log, I thought it was surely a mistake, had to be the nose gear, NOT. Most definitely a MLG problem. :eek: