Non-precision approaches...which one and why?

[matspart3]

My airfield has NDB/DME and 2nm and 0.5nm SRA capability to 'limiting' runways (c1100m). MDA(H)'s and RVR requirements are all broadly similar. Which would you choose and why?

[Max Angle]

If it's an airfield that does a lot of SRA's then it's a good bet. If not an NDB is the best bet. I have flown a few SRA's for controller training at airfields that don't do them often and most of them are not very good. Mind you some of my NDB's are not that great either. For a big a/c give me an ILS please!.

[Ignition Override]

Just be aware (maybe you are) that a large proportion of accidents during approach involve non-precision approaches. If a "modern" FMC airplane is the case, be extra cautious. Most of our approach training in the somewhat modern 757 consisted of non-precision, because of the insidious dangers if altitude capture/hold fails during VS (vertical speed) mode, resulting in a descent during a distraction...

Non-prec approaches were not considered as hazardous using the older technology, although some of us would refuse to go to a destination airport in any airplane having only an NDB approach without adequate fuel to divert to an alternate airport with an operational VOR, LOC or ILS. You might not be in the US-we don't count on the FARs (Federal Air Regs) to keep us out of trouble: how many FAA/CAA attorneys/bureaucrats have crashed and killed other people while leaning back at their desks? They watch basketball by a glowing fireplace in their homes dotting the tree-covered Virginia countryside (or boldly fly their Microsoft Learjet computer joystick) while we fly to minimums on a nasty, windy night and pray that we never land on the wrong runway (often the first approach lights which we see, due to offset runway threshholds, are the wrong ones) by mistake.

You want to bet your career/life+passengers lives on a single, very imprecise NDB pointer? But maybe you have no choice. What a lousy approach aid in the 21st century.

[This message has been edited by Ignition Override (edited 02 May 2001).]

[GJB]

ignition overide - I don't see the problem with NPA's, provided the equipment is accurate to 3-5%. and you correctly ident/interpret the beacon?

You follow the procedure, don't drop below MDH and establish visual contact.....the safety is in following the published procedure; if you can't meet your criteria you go around and have another shot or divert.

[fireflybob]

It depends a bit on the airport and the approach, etc but how about NDB/DME with radar monitoring?
As has been stated previously, standards of radar approaches do vary but one thing against SRA,s in a multi crew aircaft is all the extra RT chat which can interfere with standard crew "call-outs".

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[matspart3]

fireflybob
Radar vectors to NDB/DME FAF are available but rarely requested. I note your points about 'extra RT chat' and 'standard 2 crew calls' but I thought the (UK) SRA procedures were designed to compliment this...'Wheels' check at 8-10 miles, landing clearance at 4miles, QNH/QFE at 3, MDA/H at 2 and final advisory height at 1 before lowest OCA/H

Radar is available most days at my unit and I've monitored some awful NDB approaches ranging from the 'artistic' to downright dangerous and, as you'd expect, I'll intervene if things get really scary but it still surprises me that pilots of modern jets/turboprops (eg Lear, Citation,Dash 8 etc. landing on a short runway) will soldier on with the archaic NDB (something they probably haven't done for sometime)when radar is available. On the few occaisions that I've flown in 'real' IMC, albeit single engine, single crew, I've always plumped for SRA on the basis that one of my Radar colleagues will be planning my circuit, telling me my track distance on every leg and has a far better chance of putting me on the centreline than me with a crappy ADF and an under-used IMC rating.

Max Angle
Maybe as you suggest, the accuracy of the SRA is in doubt. I'll admit to a few of mine that have had a passing acquaintance with the centreline but I'd bet my mortgage that 99% of mine and my colleagues' SRA's will put you in a position to acquire the appropriate visual reference and, more importantly, effect a safe landing when the cloudbase/vis are close to the minima. Admittedly, the lack of practice is a cause for concern, the 1/2NM SRA is, particularly, something of a dying art...but they ain't rocket science! Left a bit, right a bit etc. etc....a bit like riding a bike...you don't forget! It's also the only part of the job where there is an end product. There's a certain satisfaction in coming out of the darkened room to find an apron full of aeroplanes that you've spent the last 2 hours 'talking down'......"happy days, jumpers for goalposts"!

[fireflybob]

>>Radar vectors to NDB/DME FAF are available but rarely requested. I note your points about 'extra RT chat' and 'standard 2 crew calls' but I thought the (UK) SRA procedures were designed to compliment this...'Wheels' check at 8-10 miles, landing clearance at 4miles, QNH/QFE at 3, MDA/H at 2 and final advisory height at 1 before lowest OCA/H<<

matspart3 - probably part of the answer to this is that because, in general, SRAs are rarely flown by (civil!) pilots the preference is towards pilot interpreted approaches. There are quite a few standard call outs on the approach (as to why - well that would be the topic of another thread!) and, my observation on a radar approach, is that these calls are invariably omitted.

On reflection though, I think you are right to say that radar should be the preferred option for the reasons that you list.

I have spent many a midnight hour in the back of the simulator watching pilots make a hash of NDB approaches. I say this with all respect because I have done the same! The fact is that we are often out of practice because often it's either an ILS or Visual!

We seem to be all getting less and less familiar with radar approaches. Years ago (yes quite a long time ago!) when I was learning to fly on the Chipmunk at a Midlands airport we often rounded the trip off with an SRA to .5 mile. We got a lot out of it and so did ATC. But then when ILS came along a lot of this went out the window!

Finally, another factor in the equation is civil/military divide - If you are ex military you have been brought up on radar and are therefore, I would respectfully suggest, more likely to use this option.

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[fly4fud]

matspart3, easy, take the one with the lowest minima and fly it on the FMS/GPS overlay, no sweat ;)

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... cut my wings and I'll die ...

[Iz]

Or fly 'em in LNAV!

[OzExpat]

There's no such thing as SRA where I operate so we always go for the most precise navaid that's available at the time. This is also spelled out in our official publications. So it's the old story ... ILS (no PAR either, of course), or VOR, or NDB, or Locator.

Obviously, if there's no ILS, we also check out the approach with the lowest MDA. This is the one that usually includes the use of DME. Of course, with the advent of GPS, we regard it as superior to VOR, in terms of tracking precision (ie none of those nasty little bends that one occasionally sees in a VOR radial. It may not, however, be superior when it comes to the MDA, so we're sometimes forced to use a less precise aid.

This is because of curious quirks associated with the location of the navaid. That is, sometimes the least precise navaid is better situated - further away from terrain - than a more precise non-prec navaid.

I guess you know all this anyway. But the one thing I'm curious about ... if SRA is available, why not use it? You say that the ATCOs don't get a lot of practice at it themselves and I suggest that this might be because pilots don't use it. Perhaps if the locally-based pilots used it more, the ATCOs would get better at it themselves, then you would all be winners.

Food for thought?

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Dispela olgeta samting i pekpek bilong bulmakau!

[Ignition Override]

Fire Fly Bob made an interesting comment which was something we experienced at New York's La Guardia doing a LOC about two years ago into a normal big, busy airport. Right when we were about to level off at MDA, Approach Control (some guy) suddenly blurted on the radio something that was not important, but they made it sound so d****d serious, just an RVR update (did not matter to us on the final approach segment, and too busy!)! We went over 50' below MDA and got right back up. What was their problem?! THAT CLOWN better not ever do that again.

If any LaGuardia ATC types don't like my remarks-that's their problem.

[critcaact]

matspart3,
All other things being the same I'd choose the approach that had the longest distance from the MAP to the runway touchdown zone. This allows a more controlled rate of descent if the WX at time of landing is actually at minimums.

NDB approaches are antiquated to say the least but a GPS or other LNAV overlay works great.

NDB at one airline I'm familiar with means "no damn business".

[Tinstaafl]

Using ground based aids & dis-allowing precision or radar approaches my choices:

Generally runway/straight in approaches 1st:

1. Localiser/DME or Localiser/Mkrs. (or similar --> Localiser type Directional Aid or Simplified Directional Facility, can't remember which is which...)
2. VOR/DME including DME arrivals if likely to become visual
3. VOR with cross bearings
4. NDB/DME incl. DME arrivals if visual is likely.
5. NDB with cross bearings

Circling types:

6. Localiser etc including the other one of LDA or SDF not in #1 above.
7. VOR etc
8. NDB etc
8. DME descent (not that there are any of those left now)


What do others think? Other factors being equal, would you prefer a straight in approach using NDB/DME? Or a circling approach with a VOR?


[This message has been edited by Tinstaafl (edited 09 May 2001).]

[OzExpat]

Tinny...

<font face="Verdana, Arial, Helvetica" size="2">DME descent (not that there are any of those left now)</font>

Still quite a few here in PNG mate, if you miss them THAT much! :) Most of the time, it's the only navaid that's serviceable! http://www.pprune.org/ubb/NonCGI/frown.gif

<font face="Verdana, Arial, Helvetica" size="2">What do others think? Other factors being equal, would you prefer a straight in approach using NDB/DME? Or a circling approach with a VOR?</font>

I can't imagine any place where there'd be such a situation, but here goes ...

The "all factors" bit is rather a sweeping generalisation. If the straight-in serves the runway I need and weather is down at minimums, then I'd take that one every time. BUT, it largely depends on how the MDA works out for each type of approach. It is usual, for example (at least in this part of the planet), for straight-in approaches to have a lower MDA than a circling approach. Sometimes, the Cat A/B Circling MDA will be the same as the straight-in MDA, but that don't happen very often here.

If weather isn't much of a problem, I'd go for the circling approach using the VOR. It really is a case of "horses for courses" but I agree with your comment about a preference for a DME Arrival, especially if covers a broad sector of tracks. Saves time ... and money (which keeps the boss happy - and me in a job!).

A situation we have at AYPY is that a VOR/DME approach serving RWY 14L has a higher MDA than either the Twin Locator for the same runway, or the Locator/DME procedure. Thus, if the ILS ain't available and the weather is at minimums, I go for the Locator-based procedures every time.

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Dispela olgeta samting i pekpek bilong bulmakau!