PSX Inertial Landing.

[Mariano]

Thanks!

[Hardy Heinlin]

Mariano, did you train this on the 767?

Were your ILS signals lost temporarily or for the rest of the flight?

I'm including four options:

- LOC signal loss for some seconds (random duration)
- LOC signal loss permanently
- G/S signal loss for some seconds (random duration)
- G/S signal loss permanently

Do you know how long the A/P remains engaged during a signal loss? Or does it stay engaged and simply keeps riding on the IRS data till the end?


Cheers,

|-|ardy

[Mariano]

Hardy,

The scenario they set up was mainly to demonstrate what happens (or doesn't happen) when ILS signals are lost.

The LOC and GS losses happened below AH (200' RA) and the sim landed and rolled out on inertial data. A/Ps remained engaged until disconnected for taxi.

Sorry I can't answer you questions from memory. I vaguely remember reading something about time limits (in terms of seconds) for signal losses. I am going to consult my notes/manuals and I'll get back to you. I am on a trip right now, but once I get home (Friday night) I will consult the FCTM for answers.

Mariano

[Mariano]

Here is a quote from the Boeing (767) FCTM.

" The AFDS includes a monitor to detect significant ILS signal interference. If localizer or glide slope signal interference is detected by the monitor, the autopilot disregards erroneous ILS signals and remains engaged in an attitude stabilizing mode based on inertial data. Most ILS signal interferences last only a short time, in which case there is no annunciation to the flight crew other than erratic movement of the ILS raw data during the time the interference is present. No immediate crew action is required unless erratic or inappropriate autopilot activity is observed.
If the condition persists, it is annunciated on the attitude display. If the autopilot is engaged, annunciations alert the flight crew that the autopilot is operating in a degraded mode and the airplane may no longer be tracking the localizer or glide slope. When the condition is no longer detected, the annunciations clear and the autopilot resumes using ILS for guidance."

As you can see, the FCTM does not specify the amount of time between the start of the signal anomaly and the time the crew is alerted. My ground school notes say that it is twenty seconds for the localizer, and fifteen seconds for the glide slope (again, those are notes from a CBT, I cannot verify with any official Boeing documentation.)

Mariano

[Hardy Heinlin]

Thank you, Mariano. During this malfunction, did you see the G/S pointer on your instruments jumping around at random, or did the system automatically move the pointer completely out of view?


Cheers,

|-|ardy

[Hardy Heinlin]

P.S.: Any idea how long it takes until an IRU track is established based on the initial ILS tracking? I assume the system cannot do IRU tracking immediately after ILS capture, it must first stabilize its virtual track. Or it computes the track using database ILS coords. But that would require FMS. The AFDS doesn't even know the exact G/S angle, it assumes a standard 3.0° angle.

[Mariano]

The failures were triggered below AH. Both pointers were still in view but showing large and fast deflections. Since we were so close to the ground, soon after the deviations began, the airplane started to "disregard" the glide slope (or in this case the "inertial glide slope") in favor of radio altimeter inputs for the flare mode. On the other hand, the "inertial localizer" was followed until autopilot disconnect, of course (I recall this was around forty knots ground speed.) It did an amazing job, although this was, in the end, a simulator (crosswind component was ten knots.)

Regarding you question about how long it takes for the AFDS to establish proper inertial tracking for both the glide slope and localizer, that is a question I have asked myself. I am going to search my books and try contacting some sim instructors.

Mariano