Get the same problem... and turn it on when the operations manual tells me to... Try to use the manuals to get the procedures right, but I guess that it's one of those things called 'a funny'...

As I've said befor, have you all checked your failures menu? I already had a Yaw Damper failure while using the Service Based Failures.

Had the same issue - no failures, IRS set, yet yaw dumper didn't want to cooperate (I didn't try FLT CONTROL B off/on thing though). The flight was successful, I didn't notice any difference actually! cheers, Jakub

Ok guys, I had no problems on my second leg and I believe the difference was that I made sure not only to switching the IRSes to NAV but also entering my position in the FMC before I switched the yaw damper ON.As for the flow and when to switch the yaw damper ON that is part of the preflight procedure according to the real Boeing doc.

At my airline the Yaw Damper is turned on after the IRS is aligned and the electric Hydraulic pumps are turned on. This is after external power is selected or the APU is started. FWIW I had it not turn on once, made the flight without it, and the problem never occurred again.

I had the yaw damper problem now as well.(Armed it after putting IRS to NAV)Trying to reset FLT CONTROL B doesn't help.RegardsMark

Edited February 5, 201214 yr by marcom

+1 had this failure today as well. with the 737-700WL. In QRH it only says that you should avoid Turbulence and set the switch to OFFFunny that it came today :-)Maybe it is a PMDG date teasing service :-)/Michael

Edited February 5, 201214 yr by Michael Moe

If you turn on the YD before ALIGN illuminates on the IRS it will remains inoperative untill flt cont switch B is set to the OFF position, this resetting the logic. (a little known bug)When you switch the IRS to ALIGN or NAV, wait few seconds (or the ALIGN light) before turning ON the YD, then it will work.NO POSITION IS REQUIRED FOR YAW DAMPER ENGAGEMENT LOGIC (neither for operation)NO HYDRAULIC PRESSURE IS REQUIRED FOR YD ENGAGEMENT LOGICNO RUNNING ENGINES.The switch needs power to the SMYD, flt cont switch position and IRS valid signal (that is given when turned on, either aligning or already aligned)

I switch the YD on after engine start and off before engine shutdown.The reason the YD requires the IRS is because it takes acceleration data from it to function.Best regards,Robin.