Different RNAV approaches 

There are 3 RNAV approach types

Those which only benefit from horizontal guidance: LNAV.

Those which benefit from horizontal and vertical guidance and are intended for baro-integrated FMS equipped aircraft: LNAV/VNAV.

Those which benefit from horizontal and vertical guidance and are intended for WAAS equipped GPS (EGNOS as well): LPV.

We shall ignore GBAS procedures which are not yet installed on a regular basis in Europe.

LNAV approach (2D)

Non-WAAS GPS systems allow for approach with horizontal guidance only. Their precision is 5 NM in Enroute mode, 1 NM in Terminal mode and 0.3 NM in Approach mode. Which is to say that when the needle just arrived at full deflection, cross track deviation is 5 NM, 1 NM or 0.3 NM depending on plane's mode at the time.

Scale transition is made automatically assuming the pilot does not intercept final approach segment at less than 2 NM from FAF, because Intercepting final approach segment at less than 2 NM from FAF, would prevent automatic scale transition.

It is pilot's responsibility to check and announce scale transition.

LNAV approach

LNAV/VNAV approaches for FMS receptors (3D)

Guidance

These approaches provide lateral and vertical guidance in the same cockpit presentation as an ILS.

Horizontal guidance

Horizontal guidance is identical to LNAV approach: their precision is 5 NM in Enroute mode, 1 NM in Terminal mode and 0.3 NM in Approach mode.

Vertical guidance

Vertical guidance relies on altimeter.

Indeed, FMS system relies on altimeter to compute arrival altitude and glide slope. That renders the system vulnerable to the same errors as altimeter's. Especially when flying in cold weather, altitude and glide are false and it is not possible to double check altitude passage because the check would rely on the altimeters as well.

Obviously, when flying an ILS, the problem is different, as ILS beam does not rely on altimeter source. 

MFO's (Obstacle clearance margins)

Obstacle clearance margins - grey zones on approach profile - are computed with reference to ATI (International Type Atmosphere) + 15°C. Obstacle clearance slope is then reduced with reference to a minimal temperature that sets the exploitation limits of that procedure. The approach is not allowed then, if temperature is at that minimal temperature and it is specified on the approach plate.

Some systems are able to compute corrections for temperature.

LNAV/VNAV and LPV approaches for WAAS receptors (3D)

WAAS GPS's receptors provide vertical and horizontal guidance for LNAV/VNAV approach (as well as FMS) and for LPV approach, if satellite constellation is enough to provide that service which means that 2 geostationary satellites have to be covering the zone.

Note: This service is essentially provided for northern hemisphere where different systems overlap.

From EGNOS - PORTAL . EU

LNAV/VNAV approach

Horizontal guidance

Horizontal guidance precision increases by steps (5 NM, 1 NM and 0.3 NM) exactly as for LNAV alone.

From GARMIN Pilots Guide 

Vertical guidance

Vertical guidance precision increases regularly, starting with a 150 m deflection at FAF down to 45 m. At which point, the beam ceases to converge.

LNAV-VNAV approach

LPV Approach 

Characteristics

LPV approaches are said APV SBAS (Approach with Vertical Guidance, Satellite Based Augmentation System) because the normal satellite constellation is increased by two geostationary satellites which for Europe provide EGNOS augmentation.

Initially, APV/SBAS provided a DH (Decision Height) in between 246 ft and 295 ft depending on terrain configuration. They may now be reduced to 200 ft (AGL).

These procedures are available to airplanes GPS WAAS equipped.

They differ from LNAV/VNAV because they provide a convergent beam pretty much similar to ILS beam.

Guidances

Horizontal guidance

Horizontal guidance's precision increases as the beam converges (according to a 2° angle) from FAF to opposite runway threshold.

Vertical guidance

Vertical precision increases regularly from 150 m deflection at FAF down to 15 m deflection. At which point the beam ceases to converge.

LPV approach

LPV approach and CAT 1 vertical guidance 

To allow CAT 1 vertical approach minima's (200 ft AGL), the airport must fulfill with precision approach structures which are the same as for an ILS approach. They are:

Approach light system.
Precision approach ground markings.
Parallel taxiway.
Obstacle free.
No intrusion into the glide slope plan.

If one or several of these criteria are not fulfilled, an LPV approach has higher than 200 ft AGL minimas. For example, minimas at Lyon Bron are 200 ft AGl as compared to minima's at Reims where LPV minimas are 493 ft AGL.

RNAV longitudinal error

RNAV systems suffer from longitudinal error, RNAV procedures are therefore built with a slope origin that is displaced upstream from runway threshold. But that does not have any consequence on aircraft flying.  

GBAS approach

They are identified as GLS RWY xx and benefit from ground reinforcement instead of satellite reinforcement.

They will allow category II and III approaches but are not actually working at least outside US and they are not planned to be in a short future. Some are working though, used for calibration purposes.

Some approaches do not exist but we fly them anyway

LNAV approach only provide for horizontal guidance and they have not been designed to receive vertical guidance.

WAAS GPS receptors may however provide vertical guidance on cockpit instruments for LNAV approaches, if geostationary satellites are operational. As a pilot, we see what appears to be a 3 D approach, which it is not. It matters because when flying LNAV approach, the primary instrument is the altimeter and not the computed glide that appears on the cockpit instrument.

That is why Garmin indicates LNAV + V.

BEFORE YOU START LEARNING

What is it all about ?

The course is divided into SECTIONS

Each section is concerned with a part of the flight : Before taxiing, Using flight instruments, Departure, En Route, Holds, Arrival, Approaches, unusual events and so on.

Each section is divided into Lessons.

For exemple, section "PLANNING FOR AN IFR FLIGHT" contains two lessons : planning weather wise and planning fuel wise.

Each lesson ends up with a Quiz.

The quiz is simple, it aims at getting things memorized, not tricking you. Read carefully and choose the most complete answer.

It is not tricky and it is not by any mean some sort of evaluation system. You can - and you should - take the quiz as many times as necessary, get back to the lesson as much as you want. But you have got to get a 100%.

So read the answers, some are obvious some are not so obvious. Some of them are right but incomplete. Once again, the quiz is a learning experience !

Note that you have the opportunity to have a look at your answers completed with eventual comments.

The length of each lesson depends on its content but every single one of them processes only one subject which has been brought to what really matters.

Do not go through as fast as you can

Don't get over the text as fast as you can to reach the quiz and proceed to the next lesson. Obviously you are already familiar with some material but keep in mind that the course is constructed as a whole and intended to be efficient as far as IFR flight is concerned. Attempting to cut through in order to gain time will end up lengthening the overall process.

If something appears that you do not know

Should you come through some concept that you don't understand, don't stuck on it, chances are that it does not matter so much at that stage or eventually - and it is generally the case - the explanation will follow rapidly. Should the explanation come up in a couple of pages, a note will let you know.

Logo's

Some PDF are available for downloading

  And above all:

Have fun, it is exciting !

It is up to you now !