NKP S2 From United States of America, joined Dec 1999, 1714 posts, RR: 6 Reply 1, posted (12 years 2 months 3 weeks 5 days 4 hours ago) and read 537 times:
The nosewheel steering bypass pin was not removed before the wave-off. The clincher is that you said the pushback lined you perfectly with the intended ( initial ) taxi out. Years ago on the 737 they just made certain the "A" system pumps were off for pushback...as pressure will try to center the gear during pushback. Newer 737's have, and older 737's were retrofitted with, a bypass valve in the pressure/return lines, located on the upper R/H part of the gear: This valve is pushed in by hand and held in bypass position with a small clevis pin. When in bypass the nosewheel steering system is not pressurized even though the "A" system is pressurized...although it is common practice for some operators to have the hydraulic pumps turned off as an added margin of safety...per checklist. FWIW, most A/C have a similar system to deactivate NW steering...either mechanically with a lever/plunger and pin or a switch in the cockpit or on the exterior. BTW, not all that rare for events like that to happen
AV8N2 From United States of America, joined Feb 2001, 39 posts, RR: 0 Reply 2, posted (12 years 2 months 3 weeks 2 days 3 hours ago) and read 498 times:
NKP hit the nail on the head there! Most (or I should say many) of the 200s are converted now to have the bypass pin removed. The 300+ have a little different set up, ie no pin.
The Bang you heard was just the pin shearing, no harm to the ac itself!
BTW, probably was a maintenance personell error, but either pilot should have caught it.
AV8N2 From United States of America, joined Feb 2001, 39 posts, RR: 0 Reply 4, posted (12 years 2 months 3 weeks 1 day 4 hours ago) and read 471 times:
Actually, I have never flown the 300. I just assumed that the 400 had the same gear...my mistake! The 200s that I fly have all been recently converted to remove the external pin, yes. The 400s never had the provision for a bypass pin, as far as I am aware of.