HAWK21M From India, joined Jan 2001, 31775 posts, RR: 55 Posted (2 years 7 months 6 days 5 hours ago) and read 2446 times:
During Maintenance.....at times a Snag message is cleared by recycling a CB if called for.....Normally its recommended that approx 5-10 seconds should elapse before the Pulled out CB is reset,to give adequate time for the circuit to Break & make positively.
Someone was mentioning 30 secs.....Is there any logic to that duration.
okie From United States of America, joined Jul 2003, 3419 posts, RR: 3
Reply 1, posted (2 years 7 months 5 days 14 hours ago) and read 2368 times:
About your 30 second question.
Hawk I can not answer for aircraft but on the industrial side we call for 20 seconds.
Most people count to 20 in about 10 seconds which normally will allow mechanical type relays and contactors to shift and also capacitors to bleed on recirculation circuits that are used on some DC coils or economisers on AC. Depending on the device some relays/contactors once they are latched will not release until the voltage drops to about 50% before the mechanical device can start to shift states.
The issues we have is that PLC or Computer driven control (they have a few seconds of ride through ability as well) when shifted from on to off to on quickly will see the relays/contactors/devices in their energised state in some unorganized sequence instead of the unenergized state or start position and cause issues within the program. Depending on how sophisticated the program is it will see the relay that has not shifted yet as a fault/welded contact or interrupt the logic to a function block because it saw the device in the wrong state.
We had one customer when told to recycle power (off for 20 seconds) would turn the power back on in about a second.
We used to joke maybe he only knew one number between 1 and 20.
fr8mech From United States of America, joined Sep 2005, 6138 posts, RR: 16
Reply 4, posted (2 years 7 months 5 days 4 hours ago) and read 2291 times:
I don't recall ever seeing a standard anywhere, but 10 - 15 seconds seems about right for our Boeings. On the McBoeing, we've adopted a 2 minute rule, especially when dealing with chapter 22, 24 or 32 issues. That 2 minute wait has really improved the RTS rate.
tdscanuck From Canada, joined Jan 2006, 12710 posts, RR: 80
Reply 5, posted (2 years 7 months 5 days 1 hour ago) and read 2270 times:
Quoting HAWK21M (Thread starter): Normally its recommended that approx 5-10 seconds should elapse before the Pulled out CB is reset,to give adequate time for the circuit to Break & make positively.
The circuit will break "instantly", that's not what you're waiting for. As others noted, you need to give the upstream and downstream systems enough time to stabilize under the new power configuration.
Tristarsteve From Sweden, joined Nov 2005, 4194 posts, RR: 32
Reply 6, posted (2 years 7 months 4 days 18 hours ago) and read 2217 times:
On the A320 series, the FCU has a stated 7 minutes c/b reset time. This is to allow a capacitor inside it to dissipate.
Another point is that many computors have hot battery back up.
I had a strange A320 FMGC problem recently, that we later believed was due to a faulty new nav data base. Anyway the FMGC would not predict times and fuel. After many tries, we turned off all the power in the cockpit so that only the green power avail light was on. Waited 30 secs, and powered up the aircraft again. When the MCDUs came back to life, the route and winds were still sitting there. To erase these you need to go downstairs and trip the hot battery c/bs. (turning the battery off in the flight deck is not enough)
Had a similar experience on a B777. Big problem with AIMS ( Display Resources ) and would not clear with all 8 c/bs tripped together and reset. (You get about 4 pages of Status messages!, that take 5 minutes to clear.)
But went down in the cellar and tripped the two hot battery c/bs as well, and it all started working again.
(But you lose all the maint computor fault history)
strfyr51 From United States of America, joined Apr 2012, 1902 posts, RR: 1
Reply 8, posted (2 years 7 months 4 days ago) and read 2115 times:
Having been a Controller for both Boeing and Airbus It particular to the type of airplane and equipment.
Airbus TSM 24-00-00-810-818 Pg205-220 will give you specifics in CB cycle time. and these should be adhered to for the best results. one in particular comes to mind FMGC resetting (on the Ground with Engines Stopped to be precise )
Get's the best result cycling BOTH the FMGC and the MCDU at the same time Open for 10-15 seconds. What it doesn't say is turn OFF the flight Directors, set the Navs to max range (or the same range) to prevent incurring the "Off Side Range Mode" Message and wait until the Triple Click before restoring the FD and looking for '1FD2' on the PFD. On the 737 many if not all CB's will reset their systems in 20 Seconds out though I used 30 seconds as a rule of thumb.
It completely depends on the Controller's Technique. If it works for you and you're successful more than NOT?
Then you do your thing !!