Talk:Required navigation performance

Angr (talk • contribs) 22:50, 22 March 2006 (UTC)

The latest revision to this article suffers from a number of misconceptions. RNP is not a technology, in fact part of the purpose of RNP is to separate navigation performance from the technology used to achieve it. It is instead a collection of standards and recommended practices.

There is an implication that RNP depends on spaced-based navigation systems but, since RNP is by definition independent of the technology used to achieve the required performance, this is not the case. It follows that the subsequent references to satellites are misplaced. The best ILS minima are significantly better than the best currently from RNP procedures and this is likely to be the case for some time to come though RNP and RNAV procedures are available which have better minima than non-precision approaches. RNP provides a very significant advantage where terrain or other factors require an initial approach which is not straight or with a few straight legs.

There also seems to be confusion between Continuous Descent Approach and Constant Descent Angle. Continuous Descent Approaches have been an objective since the mid 1970s, the aim being that the altitude of an aircraft descending on approach to a runway is to the extent allowed by other constraints such as traffic and terrain maintained in relation to the distance the aircraft has to run to the runway so that the engines can be operated at or near to idle power and without the need to increase drag unecessarily. This reduces fuel usage and engine power at low altitudes which reduces cost and is more environmentally friendly. The greatest aid to such operations has been the increasing availability of systems allowing the pilot to accurately estimate the distance remaining to run to landing. Constant Descent Angle is a technique used in flying a non-precision approach in contrast to the alternative, often called 'Dive and Drive' in which the aircraft altitude is reduced in steps during an approach to the minimum permitted at each stage of the approach and then flown level to the point at which further descent is permitted. In some conditions this may permit an early transition to flying by visual reference. A constant descent angle approach aims, as the name implies, to maintain a constant angle of descent down to minimums, which achieves a more stabilised approach configuration, long recognised as desirable in the interest of safety. Both Continuous Descent Approach and Constant Descent Angle were in use long before the advent of RNP. treesmill 18:23, 19 June 2007 (UTC)

Treesmill is correct re "technology." Edited.

Agree also that Continuous Descent is a "method" that can and has been implemented in a variety of ways (could fly by hand) but that does not negate the fact that many RNP procedures do implement it.

As for references to satellites:I think the current entry addresses theory (any sensor) versus current practice (sensor=satellite).

As for minima vs NPA and ILS: there are plenty of published RNP procedures with minima down to 250', which while not better than ILS certainly compares more favorably than Treesmill implies. Does the latest edit address this issue more crisply? Wolfeboro325 19:30, 21 June 2007 (UTC)

You are quite correct about satellite navigation. The ICAO PBN manual regards GNSS as the primary aid for RNP. I've reworded para 2 to take account of this.

Continuous Descent Approaches are facilitated by any aid that gives a reasonably accurate distance to run. A DME on the field does this, but continuous descent is not part of any description of DME. Similarly, Constant Descent Angle is characteristic of an ILS, but I've never seen a description of ILS that includes that.

Even a standard CAT I ILS will have a minimum of 200' subject mainly to terrain constraints and of course the best ILS minima are much lower. This is, as I said, significantly better than any existing RNP approach of which I am aware, so 'comparable' is misleading.

It may be worth noting that RNP procedures are usually designed with maximum capacity as an objective. It is one of the great problems of the current project to modernise air traffic management that efficiency and capacity tend to be mutually exclusive. treesmill 03:00, 30 June 2007 (UTC)

How many dimensions?

The article mentions navigation specifications within a certain volume of 3-dimensional space. The WSJ article cited below suggests—but doesn't state explicitly—that the required navigation capabilities are actually 4-dimensional: be within a particular volume of 3-dimensional space within a particular window of time (plus or minus a certain period from an assigned time). Is this part of [the / a] RNP spec?

• McCartney (May 12, 2009). "The Middle Seat: A New Route to Easing Air-Traffic Congestion". The Wall Street Journal. Retrieved May 13, 2009. The plane's autopilot can put the aircraft at an exact position within seconds of an assigned time {{cite news}}: Unknown parameter |firsrt= ignored (help)

Bongomatic 01:39, 13 May 2009 (UTC)

Re-written. Richard McDonald Woods 10:48, 23 October 2009 (UTC)

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