NORM/ALT

[forget]

Could any one explain the NORM/ALT switching on ADI’s – generic large aircraft, but I have a particular type in mind. Am I right in thinking that all inputs to the ADI’s are single and that it is the signal source which is switched, via relays. For example, with the Captain’s ADI, NORM would connect it to the No 1 INS and ALT would switch it to the No 3 INS. Assuming that the ADI was OK this switching would then give good indications. If the ADI itself were defective then switching to ALT would make no difference. Just curious.

[rerackit]

Can I suggest you read the AAIB bulletin S2/2000. This gives an explanation of the attitude switching on the 747. However, your interpretation is correct.The source of the attitude,(either INU`s, IRS`s or VG`s), are dedicated to their particular side. ie left to left and right to right. They can be switched via transfer relays to provide a crossover of information. This will be indicated to the crew by a caption. Some aircraft do not have a third attitude platform and will be limited to selecting normal or both on one. Additionally, there will also be the standby horizon which is totally independant. I hope this has been of use to you. Originally posted by forget:
Could any one explain the NORM/ALT switching on ADI’s – generic large aircraft, but I have a particular type in mind. Am I right in thinking that all inputs to the ADI’s are single and that it is the signal source which is switched, via relays. For example, with the Captain’s ADI, NORM would connect it to the No 1 INS and ALT would switch it to the No 3 INS. Assuming that the ADI was OK this switching would then give good indications. If the ADI itself were defective then switching to ALT would make no difference. Just curious.

[freddie the fish]

The NORM/ALT switch selects the source of information to be displayed on that instrument, i.e. NORM would put information from the No.1 VRU or INS onto the captaind ADI and ALT would use the No.2 VRU or INS as its source. If the ADI itself was shagged, then the captain would have to use the standby ADI.