Anybody knows what this sound in the cockpit mean ?

[caucatc]

Watch this video ,if you can open it 56ÍøÊÓƵ (http://www.56.com/u38/v_Mjc3MzgxNTU.html)
Go to the 28th second and you will hear a beep sound from the cockpit ,the sound just like the telephone ring ,what's that ? After that sound ,there was a smaller sound just like knocking something (around 30th second) and it rang twice ,I always heard this sound when pilot talked to me ,what is that ?

[caucatc]

The previous post did not show the right internet add ,this is the right one

56ÍøÊÓƵ (http://www.56.com/u38/v_Mjc3MzgxNTU.html)

[caucatc]

so strange ,the internet add still shows incorrect ,but I clicked it and it appears to go to the right page I want .

[Zeppelin]

Possibly auto-pilot disconnect

[caucatc]

The first sound is AP disconnected ,and what the meaning of the second knocking sound ?

[Right Way Up]

Caucatc,
The first sound is the autopilot being disengaged. The second sound is the "click click click" signifying a downgrade of the landing capability. The system detects a downgrade from Cat 3 to Cat 1 (lack of autoland) due to the autopilot disengagement.

[caucatc]

Thanks for you reply ,I am an ATC ,know little about the flight ,you said "downgrade landing capacity from CAT 3 to 1" do you mean ILS CAT 3 ? If the pilot disengage the AP ,I think they will not follow the ILS ,why still have ILS CAT 1 ?

[Right Way Up]

Hi CAUTATC,

The autopilot is required to fly an ILS with minima below CAT 1. Once the autopilot is disengaged the pilot can still fly the ILS manually but to Cat 1 minima. Hope this makes sense.

[caucatc]

Got it ,thanks!!:D