INS - How To Capture Course In NAV Mode

[taguilo]

Hi,

Could anybody kindly tell me how is supposed an old INS system like Delco Carousel or Litton should capture the active course when INS (L)NAV is armed?. Is it the same as in modern FMC systems, ie must be on a direct intersecting course, and with a crosstrack error below 5 nmiles, or is it quite different?

Thank you
Tom

[Erebus]

Using the Delco Carousel INS fitted to 747-200s and 300s, engage the autopilot in COMMAND, and fly a magnetic heading that will intercept the desired track. The capture of the INS track begins at approximately 7.5 miles cross track distance (XTK), or 2 dots on the HSI.
At capture, the the NAV annunciator indicates capture.
When capture occurs, the autopilot turns the aeroplane towards an intercept angle of 25 degrees to the INS course.
If the aeroplane is approaching the capture zone at an intercept angle of greater than 155 degrees, the autopilot might fly a circular course to intercept the INS course.

[taguilo]

If the aeroplane is approaching the capture zone at an intercept angle of greater than 155 degrees, the autopilot might fly a circular course to intercept the INS course.


This means that the intercept angle could be between 0 and 180...and passing out of 90 would be in fact kinda "backcourse" intersect, is this right? In this case, the ap would command a circular route off the active course until reach 25 deg of heading intercept?

Thank you for the info anyway :)

Tom

PS: Is it possible to fly a procedure turn in a CIVA INS equiped a/c?

[411A]

Procedure turns are normally flown in the AP/FD heading mode.
Not really pracatical in LNAV, with INS stand alone airplanes.