IAN Approaches

[Toga]

Can the 744 do IAN approaches?

[Hardy Heinlin]

No.

[Toga]

I thought it may have been possible with the NG FMC. Would that capability be an optional software addition or are there hardware requirements also? I know you can fly it in LNAV / VNAV but I don't know whats different under the hood so to speak.

[Hardy Heinlin]

The aircraft needs additional GPS hardware to communicate with ground-based GPS reference stations. This allows precision approaches with GPS -- without ILS. The 74-8 is fitted with that hardware. The 744 is not. The NG FMC upgrade doesn't include that additional GPS hardware.

https://en.wikipedia.org/wiki/Differential_GPS

[Toga]

Very interesting, thanks.

[dhob]

A GLS approach and IAN are two different things. The 747-8 has the capability for both, while the 747-400 with the NGFMC is not capable of either. As described, a GLS is a GBAS (ground based augmentation system) landing system which converts the GPS signals into a ILS-like approach. GLS approaches are selected in the FMC as "GLS32R" for example, and the the FMAs are identical to an ILS approach. Further the 747-8 is certified to GLS Category II autoland capability.

Integrated Approach Navigation (IAN) is a method for flying a Non-ILS approach like an ILS approach. The FMC glide path angle and lateral course are used in conjunction with the FCCs to allow the approach switch to be selected and capture the lateral course and glide path. The Non-ILS is selected in the FMC by name such as RNV07R, NDB32, LOC07L etc. The FMAs will display either FAC, LOC or BCRS as the roll mode and G/P for the pitch mode. The autopilot must be disengaged no later than 100 feet AGL.

[Hardy Heinlin]

A GLS approach and IAN are two different things.

I didn't say they were the same. I said the aircraft needs additional GPS hardware to allow precision approaches with GPS instead of ILS.

"Ground-based GPS" in particular might not be required though. So that part of my comment perhaps confused the discussion. I just think the 744 hasn't got the IAN because the companies wanted all or nothing; if GLS is still impossible, the investment in IAN may not be worth it.

Nevertheless, correct me if I'm wrong; as far as I understand the hardware upgrade, the (IAN) G/P pitch mode will not refer to barometric altitude, and the (IAN) FAC roll mode will not refer to IRU, VOR, DME, conventional GPS. As the 744 hasn't got that extra GPS hardware, the 744 FCCs got no IAN capability either.

Question:
On the 74-8, will a total GPS failure cause the FAC and G/P modes to return to LNAV and VNAV? I can imagine the IAN status will continue for a limited time based on the inertial path like autoland does in case of temporary ILS signal faults. But when a GPS failure already exists while you're pushing the APP switch, will the FAC and G/P modes engage anyway? In other words, can you start the IAN even when just a single IRU is providing position data and when, say, the left and right EFIS baro settings disagree?

In other words: When GPS fails and the captain turns the QNH up and down, will the G/P mode flight director and the IAN deviation pointer move up and down accordingly? If not, the IAN must get its altitude from the GPS -- regardless of the approach type, be it an NDB, VOR, LOC, RNAV, or GLS. -- Edit: However, it could also use the standard pressure altitude all the way down, combined with a baro additive which was recorded at G/P engagement; any further QNH change by the pilot could then be ignored.


Regards,

|-|ardy

[nosrev16]

https://www.youtube.com/watch?v=ebWYqPddI4g 

on a 737NG  the Integrated Approach Navigation     

[dhob]

Question:
On the 74-8, will a total GPS failure cause the FAC and G/P modes to return to LNAV and VNAV? I can imagine the IAN status will continue for a limited time based on the inertial path like autoland does in case of temporary ILS signal faults. But when a GPS failure already exists while you're pushing the APP switch, will the FAC and G/P modes engage anyway? In other words, can you start the IAN even when just a single IRU is providing position data and when, say, the left and right EFIS baro settings disagree?

The FMC determines current airplane flight path versus a predicted flight path. The predicted flight path is the lateral and vertical path defined in the FMC. Specifically the GP Angle displayed on the LEGS page is the predicted vertical path that an IAN glide path follows. Even without GPS, the airplane can still determine its position via IRU and DME/DME updating. With loss of GPS, an RNAV (GPS) isn't allowed. But a LOC, VOR, BCRS, or NDB approach is still flown using IAN procedures, the approach switch is armed, and FAC and G/P annunciate at capture. Procedurally, for our 747-8 fleet, IAN is the only method we use to fly Non-ILS approaches.

And yes, IAN is dependent on barometric altitude. From Boeing Aero Magazine:
While the IAN display is similar to an ILS display, there are sufficient visual differences to ensure that the crew does not confuse a non-precision IAN approach for a precision ILS or GLS approach. As on all nonprecision approaches, the altimeter is the primary method of ensuring that altitude constraints are honored.

[Hardy Heinlin]

With loss of GPS, an RNAV (GPS) isn't allowed. But a LOC, VOR, BCRS, or NDB approach is still flown using IAN ...

Fascinating. So even without GPS the FAC | G/P modes actually remain conventional LNAV | VNAV modes (technically), the only difference being the mode word cosmetics on the display.

I guess the 744 hasn't got IAN not only because of the missing GLS approach capability but also because the FCCs would probably need an update (at least in the software), and because the EFIS symbology for the PFD would require an update too. (The ND, for example, as we know, gets some additional data from the NG FMC though, but this is only possible because this data is rendered within the existing place holders. Other 74-8 features cannot be shown on the 744 ND either. Similarly, the 744 PFD symbol generator is certainly unable to display the IAN pointers etc.)


Regards,

|-|ardy

[DougSnow]

https://www.dropbox.com/s/ufqzcis46xwz2eb/747%20FCTM%20IAN.pdf?dl=0

A PDF of the IAN related pages from the Boeing Flight Crew Training Manual.