Question about VOR and NON-PRECISION APPROACH

[Timo Bruderer]

Hello everybody
Can anyone explain to me, what a VOR and a Non-Precision Approach is.
I am about to take the exam for the Swiss Virtual Airlines and i don't know what i should expect.

Thanks for your help!




<You can write your answer in german if you want>

[Chiara Paganini]

Non-Precision approaches are approaches that have only lateral guidance (they're also called 2D approaches for that reason) as opposed to 3D approaches like APVs (approach with vertical guidance) and precision approaches.
The various types are differentiade by the primary navaid that provides approach guidance, here's a list (non-exhaustive):
2D:
NPA:
- LOC DME / LOC (Primary Navaid: a Localizer)
- VOR DME / VOR (Primary Navaid: a VOR)
- NDB DME / 2 NDB / NDB (Primary Navaid: an NDB)
- RNP to LNAV or LP minima (Primary Navaid: Some sort of RNP approach capable system like IRS, GNSS etc., in case of LP GNSS with satellite based augmentation)
3D:
APV:
- RNP to LNAV/VNAV or LPV minima (Primary Navaid: Some sort of RNP approach capable system like IRS, GNSS etc. plus barometric augmentation (LNAV/VNAV) or GNSS plus satellite based augmentation (LPV))
PA:
- ILS / ILS DME (Primary Navaid: ILS)
- MLS (Primary Navaid: MLS)
- GLS (Primary Navaid: An approach capable GNSS RNP system plus ground based augmentation)
There's associated operations procedures to the various approach types that are all slightly different, so you'll have to specify what exactly you need to know.

(Also double posting is probably not the best idea...)

[Timo Bruderer]

Thank you very much for your fast reply.
So with lateral guidance you mean that the non-percision approach just helps you on a horizontal base (You have to descend manually)?

And if you still have some time, what is a winsheer escape maneuver?
If not thanks for your help.

And about the double posting: I deleted the second Post

[Thomas Wand]

So with lateral guidance you mean that the non-percision approach just helps you on a horizontal base (You have to descend manually)?

It means that you don't have a vertical guidance (e.g. a glide slope) that you can follow down. There are certain points where you can check that your altitude is correct, but no guidance between them.

Have a look at the VOR approach to runway 34 in Zurich on the vACC's homepage. You'll cross MANID at 6'000ft and then start a descent with an appropriate vertical speed (a reference table is found at the bottom right of the chart).
There is a check at EGABI (10.2 DME from KLO) where you have to be at 5'000ft. If you're higher, you'll increase your rate of descent, if you're lower, you'll typically level off until you pass EGABI. But the point is that there is no vertical guidance that leads you to cross EGABI at 5'000ft, so for example at half way between EGABI and MANID you wouldn't know if you're slightly high or slightly low (of course you can do mental arithmetics, but that's not the idea) --> you don't exactly know if you're in the descent profile, so it's non-precision.

what is a winsheer escape maneuver

A windsheer is a sudden change in wind direction and/or speed. For example, a strong headwind on final could turn into a strong tailwind, bringing your indicated airspeed dangerously close to your stall speed. Simply speaking, a windshear escape manoeuver consists of going to full throttle and climbing away the best you can - bringing you as far away from solid ground and dangerous speeds as possible. The details of the manoeuver are type-specific and should be covered in your aircraft's manual.

Think of it as a missed approach on steroids.

[Timo Bruderer]

Thank you that was very helpful!
You explained that very good. My problem is, that i want to fly for the Swiss VA and therefore i have to complete an exam. I know how to make a full flight but nothing more, thats why i am a bit worried, that i will fail the exam.
Do you have any tips for me? (for example what i should learn or practice)

Have a good evening.

[Chiara Paganini]

For the NPAs, what Thomas described there is called a CDFA (Continuous Descent Final Approach) technique, which is a newer development.

Traditionally NPAs were flown using a "Dive and Drive", or more properly called step down technique where you'd descend from one crossing altitude to the next steep enough that you'll certainly make it (diving), then fly level to the next crossing altitude (driving) where you'll rinse and repeat until you hit the MDA. At the MDA you'd fly level until you either can make out the runway environment or until you hit the Missed Approach Point (MAPt) which is the latest point where you'd have to initiate a go around.

For the CDFA technique Thomas mostly outlined the required steps, but you are definitely allowed (and encouraged) to calculate and cross check more altitudes to make sure you are on profile, for example the Jeppesen Charts have them already precalculated for every mile. The tolerance on those is +/-100ft, for the MDA the tolerance is +50/-0ft because you're not protected below it. A good rule of thumb to figure out what your rate of descent for a 3° glide slope should be is ground speed [KTS] x 5 = ROD [ft/min], i.e. if you're doing 140kts GS your ROD should be roughly 140kts x 5ktsmin/ft = 700ft/min.

As for windshear escape, I can only speak for the A32S, but I'll give a bit of an insight on how it is on that type specifically. In general, any windshear warning, be it from predictive windshear or from windshear detection, is a mandatory go around. Windshear prediction uses the weather radar and is permanently available, windshear detection uses a mix of AD and IRS data and is available in CONF 1, 2, 3 and Full, from 3sec after lift off until passing 1300ft RA and again from 1300ft RA to 50ft RA on approach. The immediate reaction for the PF is to announce "Windshear TOGA", set thrust levers to TOGA and follow SRS orders from the flight director, which will try to maintain a safe flight path. Do *not* change anything on the configuration (flaps, gear, etc.) until out of the shear, when you are run the normal GA drill to reconfigure the aircraft.

I'm not with Swiss VA, nor do I know their exams, but in general I'm very skeptical of such entry exams. If you want to learn/practice for it, the aircraft's FCOM and FCTM would be a good place to start for the questions specifc to a type, for more general questions the FAA Pilot's Handbook of Aeronautical Knowledge, the Airplane Flying Handbook and the Instrument Flying Handbook are good places to start

[Timo Bruderer]

Thanks to you aswell, for your long and productive response.
I can use every information you have given me.
I've already read something about the "CDFA" and the "Dive and Drive" and i must say its all pretty complecated but you made a good summary out of it.

And also thank you for the Links, i will take a look at them.

[Thomas Wand]

I've already read something about the "CDFA" and the "Dive and Drive" and i must say its all pretty complecated but you made a good summary out of it.

That difference is actually not too complicated: let's look at ILS 34 again.

In dive and drive, as soon as you passed UTIXO, you pull the throttle back and drop like a stone until you reach 5'000ft, then you level off. Once you pass MILNI, you pull the throttle again and drop. Results in many changes from straight and level to idle descend, many power changes and a high workload as the aircraft state is often changing.

CDFA (continuous descent final approach) means that you try to smoothen that out and arrange your descent in such a way that you just glide through all the intermediate altitudes - resulting in a pretty stable descent, stable (and low) thrust setting and low crew workload.

Is the difference clear now?

[Chiara Paganini]

Consider the two attached images, the speeds and configurations are specific to Da-42 but the concept applies in general too. I was taught not to "drop like a rock", because of passenger comfort and stress on the engines, but instead to aim for a ROD 200fpm greater than required to make the CDFA profile, so if for a continuous descent to the runway, you'd fly the steps with 900fpm
step descent.jpgcdfa.jpg

[Luca Santoro]

Thanks Luca and Thomas for this those great insights. I am also learning quite a lot over here !

I looked at the VOR28 LSZH as an example.
Small question: At the very bottom, below the minimum values, it's written " Visibility 4300m, Ceiling 1200 AGL".
I assume that if one of the 2 conditions is not met (i.e. below 4300 or 1200), the approach shall not be tried? Is it correct ?

Thanks! Luca

[Florian Hofer]

Small question: At the very bottom, below the minimum values, it's written " Visibility 4300m, Ceiling 1200 AGL".
I assume that if one of the 2 conditions is not met (i.e. below 4300 or 1200), the approach shall not be tried? Is it correct ?

Thanks! Luca

You can always try, but most likely it will end in a go-around as the last segment from DME 3.2 is visual and if you don't have the runway in sight at that point you should go around.

But that ceilling of 1200ft AGL is the less restrictive, if you are only able to acheive a climb gradient of less than 4.0% (VACC chart left side with DA(H) 3070 (1660)). In that situation the more restrictive limitation is your climb gradient making it necessary to have the ceilling above 1660 AGL and better visibility of 5000m.

[Chiara Paganini]

Approach authorization is a complicated topic and varies a bit from company to company. Basically if your airline doesn't have other rules you can always try the approach even if the weather is below minima, because at some airports the weather station is far away from the approach so conditions may be different (CAT.OP.MPA.305). However, many airlines have rules that you may not ocommence the approach if RVR/CMV/VIS is below minima at the FAF. At LAT the rules are as follows:

23.24.6.2 Commencement and Continuation of Approach
The CMD may commence an instrument approach regardless of the reported RVR/visibility, but the approach may not be continued beyond 1000 ft/AAE, if the reported RVR/visibility is less than the applicable operating minimum.lf, after passing 1000 ft/AAE, the reported RVR/visibility falls below the applicable operating minimum, the CMD may continue the approach.The approach may be continued below DA or MDA and the landing may be completed provided that the required visual reference is established at the DA or MDA and is maintained.
23.24.6.3 Ceiling / Vertical Visibility
An IMC approach may be commenced/continued down to DA or MDA irrespective of the reported ceiling / vertical visibility unless the controlling authority does not allow this procedure.