MASTER CAUTION

[Driver170 42]

Below is extracted from my QRH. Needing some help on understanding this -

 

After engine start and before takeoff, illumination of a red warning light, an amber caution light, an alert or other indication requires completion of the associated checklist. In certain cases, amber caution lights illuminate during MASTER CAUTION recall to inform the flight crew of the failure of one element in a system with redundant elements. If system operation is maintained by a second element, the amber caution light will extinguish when MASTER CAUTION is reset. In these situations, the amber caution light alerts the flight crew that normal system operation will be affected if another element fails. If an amber caution light illuminates during MASTER CAUTION recall, but extinguishes after MASTER CAUTION reset, completion of the associated checklist is not required.

 

1. What are the redundant elements

 

2. What is the Second element

 

I can't find any of this in the FCOM? I thought if something on the overhead fails or switches off it will show on the annuciator! So what is this passage actually mean...

Found this in google

 

If, during recall, an amber caution illuminates and then extinguishes after a master caution reset:

• check the DDPG or the operator equivalent

• the respective non-normal checklist is not needed

 

Pressing the system annunciator will show any previously cancelled or single channel cautions. If a single channel caution is encountered, the QRH drill should not be actioned.

 

For the first part is this just meaning the test part and the 12 annuciators should be ingored?

 

Second part what is the single channel caution?

[Stearmandriver 2,296]

There are certain systems with built in redundancy. From a pilot standpoint you don't really care which they are ahead of time. A simple example is the gps system. There are 2 gps systems on the aircraft. If one fails, no master caution illuminates until you do a recall test. Then you get the master caution, the annunciator, and the gps light on the overhead. Canceling the master caution resets all these lights, because this isn't a complete loss of gps capability, just one system. If you lost both gpss, the overhead gps light wouldn't extinguish.

 

The relevant checklists will fork at the "does light extinguish on recall" item, to direct you to proper action based on whether you've lost some capability or all of it.

 

In reality, if anything goes wrong on the ground, you can run the checklist but you're going to be contacting mx control for guidance no matter what. It's either a crew placardable item or you'll be doing a gate return. It's not like you just run the checklist and take off.

[Driver170 42]

Thanks makes sense now