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eca
11th Aug 2009, 10:09
For ILS Cat I and other Non precision approaches that use DA and MDA, if you have to perform go around, is it mandatory to start going around before reaching MDA, DA to compensate the altitude lost? or we can start going around when reaching DA, MDA?

Gary Lager
11th Aug 2009, 10:37
DA and MDA are different things and demand different techniques.

ILS Cat 1 is a Precision Approach, and so has a DA. You can begin the go-around at the DA (at the latest) so you will probably descend below the DA during the manoeuvre (I think by a max of 50'). That is OK.

Non-precision approaches (VOR, NDB, RNAV, SRA etc) have an MDA. You must not go below this altitude unless visual, so if you do not plan to fly a level segment at MDA then you need to begin the go-around a bit earlier, as you suggest.

extreme P
11th Aug 2009, 10:42
Generally speaking if you use VNAV for the non-precision approaches add 50 feet to the MDA to compensate for the altitude loss in the go-around.

carbheatout
11th Aug 2009, 10:47
VNAV or no VNAV we add 50ft to the MDA for a Non-Pres-App. Wouldn't fancy getting anywhere near MDA in VNAV in my old banger!

eca
11th Aug 2009, 15:23
It seems like for every "Minimum Decent Altitude", we have to add "XX ft" in MDA on APPCH Page to compensate the altitude lost during go-around right?

However, my colleagues argue that it's no need to add up if the state authority accept go around at MDA. Can the state overrule the Annex 6?

Anybody has any reference documents? My colleagues need "book said" :*

thanks

Henry VIII
11th Aug 2009, 15:51
my colleagues argueso they need to show where"book said"

eca
11th Aug 2009, 16:21
5 5 5

Unfortunately, they speak louder. Actually they are more senior!

Microburst2002
11th Aug 2009, 17:19
DA and MDA definitions are in the books (PANS OPS, I guess)
Adding 50 ft stems from the "ILS like" Non-precision approaches. These are flown with a constant descend angle (of about 3º) so that when reaching the MDA, you can land if you see the runway because you "are in the glideslope". If you don't see, you don't stay at the MDA waiting for the MAPt to see if you can land or have to go around, but you go around inmediately.
But doing this means that you will sink a few feet below MDA, which is forbidden because MDA is a minimum altitude. That is why they add the 50 ft, to cater for that.
Also remember that the MAPt is a point of the non precision approach but it is not a decision point. It is just the point at which the procedure starts, so you don't make any turn until overflying it. Ideally the MAPt should be the runway threshold, so it is a bit difficult to land if you become visual over the threshold at, say, 350 ft!
NPAs flown in the old "dive and drive" style are non stabilized manoeuvres.
They can be flown "ILS like" with a VNAV system or just following a distance-altitud table. You can make that table yourself, but that can be very tricky, a lot of different mistakes can be made when calculating it. It is better if your chart has that table.

safetypee
11th Aug 2009, 17:26
Individual States can deviate from ICAO standards. I don’t know the procedure involved, but the nature of the difference is published in a supplement to the relevant ICAO Annex, e.g. Annex 6 Part 1. (http://dcaa.slv.dk:8000/icaodocs/Annex%206%20-%20Operation%20of%20Aircraft/)

The question about not descending below MDA on VNAV has been discussed before – try search.
Some states have considered (may be allowing) a small descent below MDA which has been justified by a risk/safety assessment. Note that there are differences in obstacle/terrain clearance between ICAO PANS-OPS and TERPS.
IIRC, TERPS has a lower clearance and hence a descent below MDA would involve greater risk.

Microburst2002 re NPA table – please make it an Altitude / Distance table – reasons here. (www.icao.int/fsix/_Library%5CTAWS%20Saves%20plus%20add.pdf)
Emphasis on checking altitude first.

Intruder
11th Aug 2009, 17:40
It seems like for every "Minimum Decent Altitude", we have to add "XX ft" in MDA on APPCH Page to compensate the altitude lost during go-around right?

However, my colleagues argue that it's no need to add up if the state authority accept go around at MDA. Can the state overrule the Annex 6?

Anybody has any reference documents? My colleagues need "book said"
Your colleagues need to give you "book said" for "state authority"! If they cannot, then MDA is MINIMUM descent altitude! IF you think your can commence go-around at MDA without descending below MDA, then feel free.

Where do you get the "it seems"?!? What do your Flight Handbook and Operations Manual and "state authority" say?!?

Unfortunately, they speak louder. Actually they are more senior!
Then they should be more knowledgeable and able to show you the regulations they believe they rely on!

Microburst2002
11th Aug 2009, 20:13
SAFETYPEE

Didn't you have a briefer text?
just kidding, thanks for the valuable advice!

Dan Winterland
11th Aug 2009, 21:26
The clue is in the terminology. DA (Decision Altitude) verses MDA (Minimum Descent Altitude). On a descending precision approach altitude, you always make the decision at DA and without the visual references you go around. Dip below the DA is inevitable. On a non precision approach, in the old ways, we used to level off at MDA and fly level until the MAP, landing when visual references were obtained. When jets came along, pilots naturally adopted this technique, were flying level until MDA which in some cases was the beacon on the airfield which was was beyond the threshold - and then landing.

The inevitable consequences were unstable approaches and over runs. So someone came up with the idea that we should instead fly a constant descent aiming to land at the threshold , making the decision to land at the point where the 3 degree GP intercepts the MDA. problem is, if you go aound, you bust the MDA which isn't allowed because it's a minimum. So you add an aircaft allowance, typically 50' to the MDA.

If you want proof of how this works, check the Obstacle Clearance Allowances (OCAs) published for most airports. They are typically 150' whereas the CAT I minima are usually 200'. The aircraft allowance is added into the DA already, whereas the MDA has no such protection.

There is confusion out there and some folklore from people who don't know better. I usually experience the "you can't ever go below DA" from the newer guys (even TIREs) who don't understand the difference in terminology. These guys didn't fly the old level NPAs as they were consigned to history before they started flying - although I gather there are some operators who still use them. It also doesn't help that in the Approach Page on the FMS in some types, you put CAT I minima in the MDA page and CAT II anf III minima in the DA page adding to the confusion.

But in summary, you can never go below MDA and you can go below DA, providing you don't bust the OCA.

bobrun
12th Aug 2009, 02:29
I work for a major airline, and our manuals were amended a few years ago to state that: during a non-precision approach, a missed approach needs to be initiated AT or before the MDA. In the past we were adding 50ft to the MDA to avoid going below it during a go-around, but we don't do that anymore. This new procedure is in our ops manuals, approved and all.

411A
12th Aug 2009, 04:04
...and you can go below DA, providing you don't bust the OCA.

Some might be interested to know that with older straight-pipe 707's at max landing weight, the go-around maneuver from decision altitude (200 feet, for example) often resulted in the main landing gear just touching the runway, due to the slow engine spool-up times.

Legal?

Yup, then and now, even with newer aircraft....although with newer types, engine spool-up times are much shorter, so this is of little concern.

Just be sure you don't try the 'duck-under' maneuver, least your main landing gear get tangled in the frangible approach light bits.:ooh:

eca
12th Aug 2009, 10:19
Thanks for all comments :ok:

really love this board!

Mikehotel152
12th Aug 2009, 17:08
This new procedure is in our ops manuals, approved and all.

Approved by whom? Sounds like something is amiss. :uhoh:

Dan's got it right, except that OCAs are calculated by the relevant country's CAA for all licensed aerodromes the world over and are based on a careful physical survey of the approach path in order to establish the height above threshold of any existing obstacles. The chart makers - Jepps, Aerad - then throw various prescribed factors into the melting pot, including, but not limited to, aircraft category and the nature of the missed approach procedure, and an DA or MDA is established.

As already stated, a DA includes an allowance for height loss after decision to execute a missed approach, whereas an MDA does not because historically it didn't need to. The chart compilers haven't changed their calculations since these new approaches became common-place, so busting an MDA is still technically against the rules as far as I know and therefore obviously potentially dangerous...

The whole issue of CDFA/CANPA and busting MDAs was apparently debated by a JAR-OPS working party last year but with the arrival of EASA, EU-OPS have now taken up the mantle. Also, as safetypee says, there are differences between TERPS calculations and JAR-OPS calculations of the OCA, but that's a seperate issue.

Hope that helps.

MH152

hawk37
12th Aug 2009, 17:22
Seems some operators can treat mda as a da, for some non prec approaches. The following taken from

http://www.faa.gov/about/office_org/headquarters_offices/avs/offices/afs/afs400/afs420/acfipg/open/media/Hist%2004-02-258.pdf

The meat of which I have posted below

"This Bulletin provides the applicable
procedures, operating criteria, and revisions to the operator’s operations specifications
(OpSpecs), if applicable, to permit additional use of Vertical Navigation (VNAV) capability of
Flight Management Systems (FMS) for instrument approach. This bulletin defines a new
term, “decision altitude” (DA(H)) for the use of VNAV in conducting certain instrument
procedures. Additionally criteria and procedures are provided to authorize the use of the
minimum descent altitude (height) (MDA) as a decision altitude (height) [DA(H)] for certain
existing instrument approach procedures meeting specified obstacle assessment provisions"

martuus
26th Aug 2009, 13:59
I've heard that some airline create a DP , which stand for "Decision Point", from MDA for VNAV in non precision approach, as Airbus recommended in getting to grip with ALAR.

And DP may be at or above MDA depend on local authority. Sure operator have to evaluate all obstrucle clearance.

9.G
28th Aug 2009, 17:34
hawk37, you're absolutely correct in the new EU OPS all weather OPS section a new type of approach An APV operation is an instrument approach which utilises lateral and vertical guidance, but does not meet the requirements established for precision approach and landing operations, with a DH not lower than 250 ft and a runway visual range of not less than 600m unless approved by the Authority. along with usage of DA for CDFA NONE Precision approaches
1.8 APPROACH OPERATIONS UTILIZING BARO-VNAV EQUIPMENT

1.8.1
1.8.1 Baro-VNAV equipment can be applied to two different approach and landing operations:
1.
Approach and landing operations with the vertical guidance. In this case, the use of a VNAV system such as baro-VNAV is required. When baro-VNAV is used, the lateral navigation guidance is based on the RNP APCH and RNP AR APCH navigation specifications.
2.
Non-precision approach and landing operations. In this case, the use of a baro-VNAV system is not required but auxiliary to facilitate the CDFA technique as described in 1.7.2. This means that advisory VNAV guidance is being overlaid on a non-precision approach. The lateral navigation guidance is predicated on the navigation system designated on the chart.
1.8.2
1.8.2 Approach and landing operations with the vertical guidance provide significant benefits over advisory VNAV guidance being overlaid on a non-precision approach, as they are based on specific procedure design criteria, avoiding the requirement for cross-checking the non-precision approach procedure constraints such as stepdown fixes. These criteria furthermore address:
1.
height loss after initiating a missed approach allowing the use of a DA instead of an MDA, thereby standardizing flight techniques for vertically guided approach operations;
2.
obstacles clearance throughout the approach and landing phase taking into account temperature constraints down to the DA, therefore resulting in better obstacle protection compared to a non-precision approach procedure.
In general terms for Airbus drives it means FINAL APPR mode on FMA + proper codding on FMGC observing temperature limitations of The OAT at the airport is not below ISA -25°C e.g. not below -10°C at sea level and of course the whole approach is flown using stabilized technique.

Exactly for that reason some chart providers got rid of an increment of 30-50 ft on MDA. That change pertains, of course, only applicable approaches designed as CANPA and meeting the requirements along with the operator's approved procedures.
Cheers:ok:

LLLK
30th Aug 2009, 14:53
The new EU Ops should provide excellent bedside reading -

AMC 2 OPS.GEN.150:
...

3. All non-precision approaches should be flown using the Continuous Descent Final Approach (CDFA) technique. Different procedures may be used for a particular approach to a particular runway....

AMC 4 OPS.GEN.150:

...

4. The DH to be used for an approach should be the highest of: a. the minimum height to which the approach aid can be used without the required visual reference; b. the Obstacle Clearance Height (OCH) for the category of aircraft; c. the published approach procedure DH, where applicable; d. 200 ft for Category I approach operations; e. the system minimum in Table 1 of AMC4 OPS.GEN.150; or f. the lowest decision height specified in the AFM or equivalent document, if stated.

(Table 1 sets a minimum of 300ft for VOR, NDB/DME, LNAV and SRA terminating at 1NM; 250ft for VOR/DME, LLZ with or without DME and SRA terminating at 0.5NM)

AMC 5 OPS.GEN.150:

1. In order to qualify for the lowest allowable values of RVR/CMV detailed in Table 3 of AMC6 OPS.GEN.150.A (applicable to each approach grouping), the instrument approach should meet at least the following facility requirements and associated conditions:...

b. Instrument approaches flown using the CDFA technique with a nominal vertical profile, up to and including 4.5 degrees for Category A and B aeroplanes and 3.77 degrees for Category C and D aeroplanes, where the facilities are NDB, NDB/DME, VOR, VOR/DME, LLZ, LLZ/DME, VDF, SRA or RNAV/LNAV, with a final approach segment of at least 3 Nautical Miles (nm), which also fulfil the following criteria: i. The final approach track is offset by not more than 15 degrees for Category A and B aeroplanes and by not more than 5 degrees for Category C and D aeroplanes; ii. The Final Approach Fix (FAF), or another appropriate fix where descent is initiated is available, or distance to THR is available by FMS/RNAV or DME;

GM2. OPS.GEN.150A (Some 10+ pages on the topic of CDFA) including:

An approach is only suitable for application of CDFA technique when it is flown along a pre-determined vertical approach slope which follows a: i. Designated Vertical Profile: A continuous vertical approach profile which forms part of the approach procedure design. APV is considered to be an approach with a designated vertical profile; or a ii. Nominal Vertical Profile: A vertical profile not forming part of the approach procedure design, but which can be flown as a continuous descent. The nominal vertical profile information may be published or displayed (on the approach chart) to the pilot by depicting the nominal slope or range/distance vs height. Approaches with a nominal vertical profile are considered to be: A. NDB, NDB/DME; B. VOR, VOR/DME; C. LLZ, LLZ/DME; D. VDF, SRA or E. RNAV/LNAV;

Oh yes, and

GM OPS.GEN.150

Additional increments to the published minima may be imposed by the competent authorities to take into account special operations, such as downwind approaches and single-pilot operations.

So, if you fly CDFA, MDA=DA which may = OCA. This is beginning to be reflected in Jeppesen charts where they are publishing DA instead of MDA on NPAs for some European States.

Spooky 2
30th Aug 2009, 15:21
Speaking only for the US, "approved operators" can descend to the MDA before initiating the go-around or MAP. The specific approach needs to surveyed and approved for this exception to the norm. This approval is always annotated with a ball note on the Jeppesen approach plate that states that this exception is only for operators that have been approved for such and have had their OpSpecs annotated as such.

9.G
30th Aug 2009, 16:39
Spooky 2, as far as EU OPS concerns it's regulated as follows:
All non-precision approaches shall be flown using the continuous descent
final approaches (CDFA) technique unless otherwise approved by the
Authority for a particular approach to a particular runway. When calculating
the minima in accordance with Appendix 1 (New), the operator shall ensure
that the applicable minimum RVR is increased by 200 meters (m) for Cat
A/B airplanes and by 400 m for Cat C/D airplanes for approaches not
flown using the CDFA technique, providing that the resulting RVR/CMV
value does not exceed 5 000 m.

LLLK in the newer versions of charts it's depicted under EU OPS minimums. Indeed as pointed out by you AMC to All Weather does have a great deal of supplemental info however the main part is revised as well with a bunch of new terms being introduced like APV lower than standard CAT I approach, other than standard CAT II approach and finally NAP CDFA. All these innovation are being introduced to harmonize EU regs with FAA and allow lower minimums or retaining present minimums with none standard ALS.
Having said all this it's absolutely imperative to understand that those minimums are not to be used till approved by the relevant authorities and the operator has established proper operational procedures listed in OM as well as crews have received appropriate training.
Cheers :ok: