Continous Descent Approach – CDA
Approaches to an airport using a continuous descent, dispensing largely with horizontal flight segments and in which the engines are “idling”, i.e. working with no or very little thrust, come under the heading of CDA – Continuous Descent Approach. They end when the approach with the aid of the instrument landing system begins. CDA saves aviation fuel and reduces noise.
CDA has been in use at Frankfurt Airport for some years now during the night, in general from 23.00 to 05.00 hrs. The approaching aircraft are led onto a holding pattern at an altitude of 7000 feet (ca. 2100 m). The distance of this holding pattern to the runway threshold corresponds to an approach angle of 3 degrees. From the holding pattern the aircraft are led to the instrument landing system which begins at an altitude of 5000 feet (ca. 1500 m) and not only at 4000 or 3000 feet.
In practice, however, there is a range of factors which means that an ideal CDA to the full extent is not possible and not all approaches are flown as CDA. The use of CDA is also restricted by the fact that in an ideal CDA for the respective aircraft, the vertical profile varies depending on the type of aircraft, load, weather etc. and is thus not precisely determinable by the air traffic control. In the dense air traffic in the proximity of the airport this dispersal means that due to the imprecisely determinable profile more airspace has to be held free for the aircraft so that fewer usable altitude bands are available. This leads to limitations in the capacity. This is why the use of planned continuous descent profiles takes place at off-peak times. With the implementation of the noise abatement packages the continuous descent approach practised up to now will continue in use. The frequency and the precision of use are to be optimised in two steps:
| In the first step this is to be achieved by a “distance to go” notice by the air traffic controllers to the pilots. The intention is to increase the capacity utilisation of the CDA procedure whereby air traffic control provides distance information to the pilots to support compliance with an optimum CDA profile.
| After the start-up of the new NW runway, in a second step a so-called “transition and profile” procedure is to be established. By specification of descent profiles and courses, the degrees of freedom for the air traffic controllers are to be made more easily calculable. The basis for this is the introduction of navigation procedures which contain both lateral and vertical guidance. It is expected that this will increase the manageability of the continuous descent approach even in times with more air traffic and the procedure can also be flown at higher air traffic densities.
Schedule for implementation:
"Distance to go" information from the air traffic controllers to the pilots: several months
"Transition and Profile": after start-up of the NW runway
Dedicated Runways Operations DROps
In the course of this measure, take-offs or departures will be bundled on certain runways and departure routes in such a way that the lowest burden is generated overall. As this is a noise-distribution measure, special attention must be paid to any additional local burdens. The investigations have shown that around 50 percent usage of the DROps concept provides the best overall result for the highly burdened population, i.e. low local additional burden compared with the unchanged operating concept, but also that significant reductions of the burden can be achieved in many parts of the region.
The measure can only be used in off-peak times during the night, but is to be applied for as many departures as possible (at least all departures from 23.00 to 05.00 hrs). On uneven dates DROps is to be used, and on even dates the conventional operating concept, so that the persons affected have temporary breaks from the noise. It is not planned to change the operating concept during the night, but this may be necessary for operational reasons (e.g. closure of the runway).
The DROps concept for east operation provides for an alternative operating scenario, whereby in the off-peak night hours, all departures take place on the West runway. An additional departure route running to the east of the airport in the north direction was defined for this purpose. This is to avoid unnecessarily long flight paths and the resulting emissions while at the same time the link to the airways network is optimised.
The DROps concept for west operation provides for an alternative operating scenario whereby the departures are handled by the parallel runway system instead of using the West runway. In addition to this, in a further, not yet fully elaborated step, in the second half of 2010 it is to be examined whether a new departure route can be developed to avoid overflights of Büttelborn and other localities affected by departures on the West runway. Further optimisation potentials for DROps are also to be examined.
Schedule for implementation: end of 2010
Segmented RNAV (GPS) Approach
In this measure, satellite-based approach procedures were defined for both operating directions (west and east). Accordingly, the aircraft are first led south of the extended runway centreline and only turn onto the extended runway centreline in the direction of the runway course at around 5 nm (ca. 9.3 km) before the landing point. This means that flights can be diverted away from settlement areas in the end approach phase (Mainz, Offenbach, Hanau). The measure has an impact on capacity and is to be tried initially at off-peak times during the night. In advance of trial operation, the capacity impact and thus the possible utilisation periods for the procedure are to be investigated (up to now 23.00 to 05.00 hrs is assumed). In order to be able to use this procedure, the aircraft require special technical equipment and approval for area navigation. According to the evaluations carried out, at least 80 % of the aircraft of the airlines which fly at night fulfil the technical requirements.
It should also be mentioned that it was possible to integrate the low-noise arrival procedure CDA (continuous descent approach) practised up to now in the new arrival procedure so that these burden-lessening effects have been retained.
Schedule for implementation: End of 2010
Raising the Approach Angle
As standard, approaches are flown at an angle of 3.0 degrees. If you raise this angle, i.e. approach at a steeper angle, the distance between the aircraft and the settlement areas over which it is flying is also increased. This makes it possible to reduce the noise burden on the population. On the basis of simulation results we assume that the slightly changed angle also leads to other reductions in noise. There are uncertainties, however, as to whether changes in the time of extending the flaps or lowering the landing gear below the flight path could not also increase the noise levels. This is why this measure is first to be tested in trial operation accompanied by a measurement program. The measure is associated with various restrictions so that it cannot be used at all times or on the whole runway system. For example, for safety reasons the steeper angle can only be flown when there is no tailwind and when weather conditions are good. According to evaluations, in west operation (i.e. take-off in the west direction, landings from the east, so-called operating direction 25) that will be possible during around 60 % of the operating time, in the case of east operation (i.e. take-off in the east direction, landings from the west, so-called operating direction 07) in almost 100 % of all cases. So-called instrument landing systems (ILS) are still required for landings. A wireless signal is sent for the respective approach angle which is received by the approaching aircraft and allows it to fly in on this angle as precisely as possible. As the conventional angle of 3.0 degrees still has to be retained for landings with tailwind and poor weather conditions for safety reasons, there have to be two ILS for landings on a runway, one for 3.0 degrees and one for the increased angle of 3.2 degrees. For various reasons this is not possible for the new NW runway. In the long term, however, it may be possible to dispense with the use of the ILS due to modern satellite-based navigation technology. At this as yet unforeseeable time it would be possible – if the measure proves itself in trials – to land on the parallel runway system with steeper approach angles. As the use of an increased approach angle for noise abatement reasons does not conform to ICAO regulations, an exceptional permit will have to be granted by the BMVBS before the measure can be introduced. Schedule for implementation: after start-up of the new runway |
Conversion of Lufthansa’s Boeing 737 fleet
Since1999, Lufthansa, along with the German Aerospace Center (DLR), has carried out numerous research and development projects. The aims of these projects included, among other things, the identification of noise sources on the aircraft by overflight measurements, the trial of low-noise modifications to the aircraft, and collaboration with manufacturers in the development of retrofit solutions. A noise abatement measure for the Boeing 737 with CFM-56-3 engines is now ready for implementation. The replacement of twelve acoustic panels at the intake of the engine makes both starts and landings with this aircraft quieter. During take-off up to thrust cutback at 1500 feet a noise level reduction of around 0.5 DB is achieved, in the further course of the flight the noise level is reduced by around 1.5 dB. In the interim and end approach, the conversion allows a noise level reduction of up to 2.4 dB. Lufthansa has decided to implement this measure by the end of 2011 for its B737 aircraft stationed in Frankfurt.
Schedule for implementation: End of 2011
Optimisation of the change in operating direction depending on the tailwind
The take-off and landing direction (operating direction) is basically determined by the wind direction, as aircraft generally land and take off against the wind. As it is not possible to permanently change the operating direction, in particular in the case of changeable or “turning” winds, landings are also possible up to a certain degree with a tailwind component. The current limit is 5 knots tailwind, corresponding to around 9 km/h. Experience shows that the operating direction is sometimes also changed in the case of even lower tailwind components.
As, to the west of the airport, some residential areas are very near the airport and landings require especially low overflights, attempts have already been made to approach the airport whenever possible from the east, and to take off to the west (west operation, so-called operating direction 25). In the average over several years, this applies to around 75 % of the operating time.
Attempts are being made to increase the proportion of flights with operating direction 25. This is to take pace in two steps:
| In an initial step the existing arrangements according to which landings can be carried out at a maximum of 5 knots tailwind are to be better utilised. For this purpose the experience regarding the stability of the landing approaches are to be evaluated. The potential in terms of the additional operating days at operating direction 25 that can be achieved is currently being examined.
| In a second step the admissible tailwind component is to be raised to 7 knots (ca. 13 km/h) so that approaches from the east can take place more frequently. As the tailwind component approved by the ICAO is exceeded, the approval of the BMVBS/BAF for an exception first has to be acquired. The DFS has had a safety evaluation carried out for this purpose. Taking into consideration risk-reducing measures, this evaluation identified risks which the DFS and Lufthansa categorised as generally acceptable. The pilots’ association Cockpit rejects the measure
Schedule for implementation: 2011
Vertical optimisation of take-off procedures
The optimisation of take-off procedures pursues the aim of gaining higher distances from the residential areas at a faster pace. At the same time, the measure has the advantage that the take-off routes can be maintained more precisely. Vertically optimised take-off profiles were examined for all flight routes as to whether, given the settlement structure, it would be advantageous in terms of noise abatement to use them here, as this measure also has a noise-distributing impact. For most of the routes the result was positive so that speed restrictions were developed for these routes. These maximum speeds mean that the thrust through the engines has to be converted to altitude more quickly, i.e. that the aircraft ascends at a somewhat steeper angle. The optimised take-off procedures are to be used both day and night.
Some take-off routes in the south and south-east direction at operating direction 25 (take-offs from the runways 25 R / 25 L and 18 W) were already optimised in terms of the take-off procedures in the year 2008.
For the further implementation, the take-offs at operating direction 07 and from the West runway are to be flown with optimised procedures in a one-year trial. In the course of this it will also be examined whether the height gains expected from the speed specifications are actually achieved and whether they also lead to the expected noise abatement.
Schedule for implementation: at the latest by the end of 2010
