Can you fly an ILS app with LNAV/VNAV?

[SkyWagon737]

Hey Guys;

I have been looking for the reason why I cannot fly an ILS approach with LNAV/VNAV, I mean legal reasons. We can only fly ILS app with LNAV/VNAV for training purposes with VMC only, due to company SOP. I must say, when I compare the Localizer and LNAV during training flights, LNAV brings us offset , but the value is %5 of expanded NPS of LOC, negligible.

Thanks in advance.

[Baywatcher]

If you have the ILS selected and stay within the parameters you can select any mode.more simple to carry out a pure ILS app!

[reynoldsno1]

Alarm limits - 1 sec for an ILS, ISTR

[JosuaNkomo]

Right.


If you have raw data LOC and GS. You can fly ILS using any mode of automation or take the Automatic Aids out and do it manually. Respect limits and minima.


Obey SOP.


Close thread.

[galaxy flyer]

You might check the AFM, many have specific prohibitions on crossing the ILS and LNAV/VNAV presentations. For one thing the ILS trajectory may differ in detail from the LNAV/VNAV, LNAV does not narrow the angular path as the ILS does. Inventing procedures in aviation is rarely a good idea.

[SkyWagon737]

Thanks for the all answers, and sharing your time.

I must echo loudly that I have no intention invent anything and fly out of SOP. The problem is that once we had a warning light which prevented us from flying an ILS app (QRH) and the guy flying with me wanted fly ILS app with LNAV / VNAV during IMC, and I objected. Instead we flew a VOR/DME app.

[cosmo kramer]

once we had a warning light which prevented us from flying an ILS app

...a coupled ILS approach, or ILS?

If the ILS receiver is working and the restriction is on the autopilot, I can't see a reason why you can't fly it with LNAV/VNAV(or V/S), or manually.
Higher minima might be required, as the FD is not providing you with ILS guidance - comparable to raw data.

If the "warning light" (more details please), concerned the ILS receiver, then not a good idea.

[SkyWagon737]

WARNING LIGHT : AFT OVERHEAD PANEL "ILS LIGHT", An ILS approach, coupled with LNAV/VNAV .

[RAFAT]

The following lengthy CAA document (for private and general aviation aircraft) might help answer your questions as it explains the complex nature of LNAV/VNAV approaches and the approvals needed.

If you don't like pneumonics then don't look!

CAP 773

[Denti]

LNAV does not narrow the angular path as the ILS does

That depends on type. Some do.

[MD83FO]

on the A320 you can't fly an ILS in LNAV (managed NAV) mode beyond the final approach fix. it has to be in heading or track mode if coupled not available.

[Jetjock330]

The VNAV will use the true altitude not corrected for temperature. On a hot day in Jeddah or elsewhere, you will parallel your Glide Slope and perhaps land up 150ft higher above the the thresh hold. Not a good idea at all. Or perhaps break minima half way down the runway.

[aterpster]

The final approach segment of an ILS must be flown with ILS data. There are no exceptions. It's issues of sensitivity, integrity, and alerting.

If you couple up to LNAV/VNAV on an ILS approach, the ILS raw data still must be monitored. So, why not couple up to the ILS in the first place.

[SkyWagon737]

Of course fly ILS with ILS , that is what I defend aterpster, but for now trying to find the reasons, mental math and hangar talk. The book says good says.

[cosmo kramer]

If the failure is just "do not arm APP" or something like that, you can fly the ILS anyway you want: manual/FDs off or LNAV/VNAV or HDG select / V/S. As long as you follow the raw data obviously and is prepared to intervene or go around.

Just remember to raise the minimums to raw data minimums, if necessary, as you no longer have ILS FD guidance. 750 meter RVR instead of 550, But not sure if that is EU ops or my company SOP (too lazy to look it up).

Personally I would just click it out and switch the FDs off, 750 meter RVR is a lower minimum than the VOR in any case.

[Skyjob]

Approach Applications which are classified as RNP Approach (APCH) in accordance with ICAO Doc 9613 Performance Based Navigation (PBN) Manual (and ICAO state Letter SP 65/4-10/53) give access to minima (on an instrument approach procedure) designated as:

• LNAV (Lateral Navigation), a Non-Precision or 2D Approach with Lateral only navigation guidance provided by GNSS and an Aircraft Based Augmentation System (ABAS). Receiver Autonomous Integrity Monitoring (RAIM) is a form of ABAS. Lateral guidance is linear with accuracy to within +/- 0.3 NM parallel to either side of the final approach track.
• LNAV/VNAV (Lateral Navigation / Vertical Navigation)
  This is a 3D Approach Procedure with Vertical Guidance (APV). The lateral navigation guidance is provided by GPS and Aircraft Based Augmentation Systems (ABAS) such as RAIM in the same way as for LNAV. The vertical guidance is provided by a Barometric Altimeter. This type of approach is commonly known as APV/Baro VNAV. Lateral guidance is normally linear with accuracy to within +/- 0.3 NM parallel to either side of the final approach track. Some aircraft systems may provide angular guidance, however, and pilots should be aware of the display format of their system.
  Vertical guidance derived from the barometric data in the Flight Management System (FMS) is based on normal altimetry and any displacement from the indicated glidepath represents the same altitude error throughout the final approach. This is fundamentally different from the angular indications such as on an ILS glidepath.
• LPV (Localiser Performance with Vertical Guidance): an Approach Procedure with Vertical Guidance (APV). The Lateral and Vertical guidance is provided by GPS and SBAS. Lateral and vertical guidance are angular with increasing sensitivity as the aircraft progresses down the final approach track; much like an ILS indication.

Let us first ask if the author was discussing the LPV or LNAV/VNAV scenario.
Both are overrated in LNAV/VNAV MCP selection, but only LPV behaves "like" an ILS and thus could be flown "like" an ILS due to its angular guidance and increasing sensitivity.

[Capn Bloggs]

The problem is that once we had a warning light which prevented us from flying an ILS app (QRH) and the guy flying with me wanted fly ILS app with LNAV / VNAV during IMC,

He's an idiot. Does everything have to be spelt out?? Some level of commonsense is assumed in this job.

[aterpster]

Denti:

That depends on type. Some do.

Speaking of only U.S. TERPS, the lateral limits of all LNAV or LNAV/VNAV IAPs do reduce in width from the FAF to the runway, but not anywhere near the lateral reduction of ILS or LPV/LP. I am referring to protected airspace.

Now, if you are speaking of avionics performance, some WAAS avionics increase the lateral sensitivity to ILS-like widths at the runway, but the integrity and alerting remain at LNAV specs: +/- 0.3 n.m. ILS and LPV/LP are far narrower than that at the runway.

[Denti]

Check out IAN, and yes, integrity monitoring remains at the required RNP (down to 0.1NM, whatever you enter as RVNP), but vertical and lateral deviation indication is similar to an ILS. It is designed to be flown down to CAT I levels. But i would be careful with that, as the vertical path is based the QNH of the side with the active master FCC.

[oggers]

I have been looking for the legal reasons

Try this: the requirement is to fly the approach for which you have been cleared, using the equipment specified on the plate for guidance. In this case ILS. If you do not have the ILS guidance there in front of you it isn't 'legal'.

If you do have the ILS for guidance then you may use any other equipment you like as an 'aid to situational awareness' but not as a substitute for the primary guidance.