A330: why is the mechanical towing limit for the NWS less than the handwheel?

[sparrowwalker]

Hi all, new to the airbus.

According to my FCOM, during towing max Nosewheel travel is 65 degrees, but the description says we can control the handwheels for the NWS up to 72degrees. Wanted to ask why is the towing more limiting?

Best regards and safe flights to all

[STBYRUD]

It's a guess, but I would say structural considerations? Pulling or pushing on the nose gear at an angle is different from using it to steer the aircraft while taxiing.

[HOVIS]

Structural integrity I think. Isn't there an over limit sensor that sets a warning light in the cockpit?
It's been a while since I worked the 330.

[Uplinker]

NWS on the Airbus FBW is steer-by-wire, that is, there is no mechanical connection between the tiller and the nose gear, but it has sensors and feedbacks to prevent the nose-wheel angle going too far, which prevents damage, even if the tiller is moved further.

The tug has no electronic limitations itself, and the driver could easily force the nose-wheel too far round. I cannot remember if ECAM brings up a steering angle caution when under tow - never having seen it in practice.

That or the limit lines painted near the nose-wheel are to stop the tug driver going too far each side, and the lower angle limit presumably provides a safety margin, allowing a slight overshoot while the driver realises and corrects.