Bypass pin during pushback

The Witches Cat

Could someone tell me why it is important to connect the bypass pin before you connect the towbar when pushing back an aircraft. Thanks

Irish Steve

If it's not connected, the tug will be unable to steer the aircraft during the pushback. The pin disables the (normally hydraulic) steering system. If the pin is not in, the most likely outcome will be a broken shear pin in the towbar, which makes it impossible to continue the push back until the broken part has been replaced.

If the pin is not in and one of the flight crew turns the steering on the flight deck, the towbar can (and does) act like a scythe, and flatten anyone that's within the arc of the bar.

A long time ago now, during a dispute, the ramp manager was "assisting" on the ramp, and pulled the pin before the bar had been disconnected from the nosewheel, 2 of the ground crew were flattened by the bar as it swung through about 50 degrees to straight ahead position. Fortunately, the tug had been disconnected. No serious injuries, but to all concerned, it emphasised the importance of the people doing the job knowing what they were doing, and why.

View Profile

Yeah as Irish Steve said, it disconnects the pilots tiller (what he uses to turn the nosewheel during taxi) so as not to dismember groundcrew.
On the flip side from what Steve mentioned ;If a pushbike man leaves the bypass handle in the disconnect position, the pilot will taxi away oblivious to the fact that he can't turn the aircraft.

conor_ie

Once the pilot has told the headset man they are cleared to disconnect the headset they have to show the bypass pin to the flight deck

Bussywussy

View Profile wrote: »

Yeah as Irish Steve said, it disconnects the pilots tiller (what he uses to turn the nosewheel during taxi) so as not to dismember groundcrew.
On the flip side from what Steve mentioned ;If a pushbike man leaves the bypass handle in the disconnect position, the pilot will taxi away oblivious to the fact that he can't turn the aircraft.

The Airbus has an ECAM memo message if a steering pin is in...that's not to say someone has never forgotten to take it out...

billy few mates

I’m old enough to remember when the NWS bypass valve was modded in to 737s.
Before that you had to ask the crew to deselect the B system hydraulics for the push otherwise the tow bar would break when the engines started and the EDPs started delivering hydraulic pressure.

Stovepipe

there were aircraft that required the torque link at the back of the noseleg to be split by pulling out a pin, to allow the tug to push or tow from a wider angle. On some older aircraft, the action of the towbar moving also moved the rudder pedals, so anyone riding in the cockpit had to be warned to keep their feet back.