Just Flight Standard VC10 Operation Manual page 49

ALIGN
This begins the process of getting the aircraft's position locked in place within the system. Here the API is
assessed and in order to bring the system online, the various modes are run through.
First is Mode 8, which begins with a battery test along with a basic alignment to the horizon. During the test the
BAT light will illuminate. Once the light has gone out you can begin entering your position. If you wish to perform
a 'Quick Align', you can switch the selector to NAV, enter your co-ordinates, then return the selector to 'ALIGN'.
Modes 7 and 6 check the aircraft's position relative to true North. To move to Mode 6, you need to enter the
aircraft's current position. It then takes this position and checks it against other internal data. If all is well, Mode 5
is entered.
Reaching Mode 5 shouldn't take longer than eight and a half minutes. Mode 5 means that the aircraft's NAV
systems are now ready for use. The 'Ready NAV' light will illuminate and the number 5 will be displayed on the
CDU if set to DSRTK/STS.
Modes 4 to 0 are essentially more self-calibration. As the data is refined, the modes drop from 4 to 0. From
Mode 5 to 0 should take no more than 17 minutes, with each successive mode taking around 3 to 4 minutes to
complete its calibration.
NAV (navigation)
When the system is aligned and ready, you can select NAV mode. There are two types of operation in NAV mode:
'Normal Inertial Operation' and 'Aided Inertial Operation'.
Normal Inertial Operation allows each INS to work independently. Each system uses its internal data to confirm
its position. The position can also be manually updated by the crew when the aircraft passes a known reference
– Aided Inertial Operation. If one or more DME stations are within range, either or both INS systems can be
automatically updated.
ATT
This mode effectively shuts down the system. The internal computer and CDU displays are non-operational.
This mode is used at the pilots' discretion if they feel the data has become unreliable. Both attitude signals and
headings remain unaffected. If ATT is selected, however, the system cannot be put back into NAV mode as it
needs to be realigned and alignment can only take place on the ground. For this reason ATT is seldom selected
unless it's quite clear a failure has occurred.
VC10 Professional – Operations Manual
49