Tests at Frankfurt airport of steeper approach path at 4.5 degrees – details awaited

It has been reported that there have been some test flights of planes at Frankfurt airport, using steeper approaches. This is in order to try and reduce the amount of noise suffered by people living under the flight paths.  At Frankfurt there have been sustained and massive protests, almost weekly, since the opening of the new runway, as people have been furious about the noise to which they are subjected. The trials took place on 17th September and involved a Boeing 767 which made 7 practice landings using an approach slope of 4.5 degrees, rather than the usual 3 degrees. It seemed that there was little change in the noise reported in places less than 6 or more kilometres from the runway, but there may be some benefit for those further away. A report to the UK Parliament Transport Select Committee earlier this year gave details, from BALPA, of the practical difficulties for pilots of trying to land on a 5.5 degree slope, rather than the 3 degrees, for which most commercial planes are designed.



Frankfurt airport and suburbs

Map showing location of Frankfurt airport (to the south of Frankfurt) and some of the suburbs overflown, to the south west – Raunheim, Florsheim, Russelsheim.

Steeper approach not noticeably quieter

9.10.2013 (Die Welt)

[Bad translation from the German)

Original article in German at http://www.welt.de/regionales/frankfurt/article120777270/Steilerer-Anflug-nicht-merklich-leiser.html

Aircraft noise opponents hardly hope to mitigate the effects of a steeper approach as it has been tested at Frankfurt Airport.

First "approach steeper» flown to Frankfurt
  • Aircraft noise opponents hardly hope to mitigate the effects of a steeper approach as it has been tested at Frankfurt Airport. According to the initiative against aircraft noise Mainz is uncertain when this method could be used. “It may take a decade or never applied,” the club said on Wednesday. “There is not noticeably quieter in Florsheim, high, Rüsselsheim, Raunheim and Frankfurt south certainly not.” Also in Mainz will make no difference.

4.49 degrees in the landing place at most 3.2 degrees

The steeper approach (“Steeper Approach”) to the Frankfurt airport had been tested for the first time last Friday. A Boeing had the northwest runway served seven times at an angle of 4.49 degrees. The aircraft are to fly higher prior to landing, so less noise comes down to a few kilometers. So far, the approach angle is 3.2 degrees. Monitoring stations recorded the noise levels on the ground. The evaluation should be available in late October. The test is part of a research project of the Forum Airport and Region.




* New * 05.10.2013: Tests for steeper landing approach successfully

The recently announced tests for a steeper landing approach (see 17/09/2013 entry) took place today, with great interest the media. The runway has been repeatedly with a Boeing 767 with an angle of 4.5 degrees (instead of the normal 3 degrees) served and noise measurements were carried out. The leaders spoke of a success, the pilots apparently had no problems. First viewing of measurements in 10-15 km from the runway apparently made ​​no sweeping effect, but one hopes for greater noise reduction further away from the airport, where the gain in altitude would be very clearly (eg in Hanau).Located close to the airport cities will not help with the process, namely the last 9 kilometers are covered on the normal glide path. More: Report at hr online video , video in today journal , press release of the FFR . The analysis of noise measurements should take about 4 weeks. Could go to the procedures in “real life”, but will probably still take many years.Experts from the noise opponents have little hope that the steep approach in Frankfurt will be used nationwide.





Evidence from BALPA ( the British Airline Pilots Assocation) on 4.2.2013 to the UK Parliament’s Transport Committee said:


Further written evidence from the British Airline Pilots’

Association (BALPA) (AS 58A)

1. The British Airline Pilots’ Association believes that the following supplementary evidence may be of interest and use to the Committee in its current Aviation Strategy inquiry. In particular, this supplementary evidence is in response to the oral evidence given to the Committee by Mr Richard Deakin of NATS on 10 December 2012.

2. The standard angle for glideslopes is universally set at 3 degrees with variations typically between 2.5 and 3.25 degrees to accommodate local circumstances such as airspace restrictions and close in ground obstructions. A 5.5 degree glideslope, as proposed by the NATS Chief Executive, Mr Richard Deakin, is exclusively used at airports where a normally inclined approach path is precluded because of terrain as in mountainous areas or obstacles such as the high rise buildings that surround London City airport. Because of the stringent requirements on aircraft performance and certification, and crew training in special procedures, 5.5 degree glideslopes are not generally considered appropriate as a means for alleviating local area noise disturbance. Where these steeper slope approaches have been adopted they have only been available for smaller aircraft types ranging up to Airbus A318 size and have never been used by bigger commercial air transport (CAT) types let alone the wide bodied long-haul aircraft types that predominantly operate in and out of London Heathrow.

3. For large aircraft the problems of approaching on a steep glidepath can be considered under the headings of operation and organisation:

Operational Issues

4. Speed stability. The inertia of heavy aircraft means that it is very difficult to accurately control approach speeds on a steep approach particularly when the airspeed has increased due to correcting to the glidepath from above. Use of airbrakes with landing flap is prohibited on most large types. Furthermore, the increased use of drag inducing configurations, possibly against thrust to allow higher engine power settings, would introduce issues of aircraft structural fatigue.

5. Engines at idle power. To achieve a steep glidepath heavy aircraft would need to have their engines set at or near approach idle power with the consequence that, in the event of having to go around (GA), with big, high bypass engines taking longer to spool up, the height lost between GA initiation and the aircraft beginning to climb away would be correspondingly greater. This is exacerbated by the fact that the aircraft is already descending faster therefore greater anticipation of having to GA would be needed. For the same reasons approach minimums would have to be set higher to ensure aircraft aborting their approach did not bust obstacle clearance limits with the knock on effect that, in poor weather, many more aircraft would require to GA.

6. “Sink Rate” EGPWS alerts. At a typical heavy aircraft approach speed of 160 IAS the rate of descent on a 5.5 degree glidepath would be around 1600 fpm which normally would be classified as an unstable approach and would be above the threshold for triggering an EGPWS “Sink Rate” aural alert.

7. All Weather Operations. A 5.5 degree glideslope is presently not compatible with an autoland profile and would require a significant certification effort to make it so if, indeed, it was possible to retrofit to current aircraft types. Such an operational restriction would be a major impediment to the all-weather capability of an airport.

8. Engine Out Approaches. All engine out approaches are predicated on a 3 degree or close to 3 degree glidepath. It would be impractical and add complication to introduce different contingency procedures for engine out approaches to accommodate the very few airports where steep approaches were in operation. Such airports could not be planned as alternates.

9. Flare/Roundout Manoeuvre. The transition from a 5.5 degree glidepath through to touchdown on the runway would be an abnormally challenging manoeuvre to fly which would require special training and would involve higher risk when compared to a landing off a normal 3 degree approach. The potential for “heavy” landings would necessitate the imposition of lower maximum landing weights and increased engineering maintenance of landing gears. Other risk mitigating measures might involve the setting of lower crosswind limits further limiting the availability of the airport to operators. Some aircraft types, particularly larger widebody types, would be more susceptible to tail scrapes. The complexity of the roundout manoeuvre combined with the normally acceptable variation in piloting skills would very likely result in a greater variation in touchdown positions and speeds with a contingent increased risk of “floating”, long landings and runway overruns as well as a potentially significant impact on runway occupancy rates and therefore runway capacity.

10. Tailwinds. Whereas on normal approach paths tailwinds of up to 10 to 15kts can be accommodated to allow a certain amount of operational flexibility in the choice of runway direction, with steep approaches no such flexibility could be tolerated.

Organisational Issues

11. Crew Training. Special crew steep approach training would be required for any approach steeper than that currently used.

12. Aircraft Modification/Certification. Significant aircraft modification (landing gear, flap/spoiler operation- fly by wire flight control law reprogramming , EGPWS reprogramming) would be required together with an extensive scheme of type certification for steep approaches.

13. Airport Availability. For several reasons (as stated above) an airport serviced by 5.5 degree glideslopes would be much more weather dependant in terms of cloud base, visibility, and wind and therefore would suffer a greater degree of weather closure events than would be the case with a normally inclined approach path.

14. In summary the introduction of 5.5 degree glideslopes would present substantial difficulties for both aircraft and airport operators. The former would be burdened with, initially, aircraft modification and certification costs and then recurring crew training and aircraft maintenance costs. The latter would not be able to boast a year round, 24 hour, all weather operational capability necessary to support scheduled CAT services. The likely upshot would be that aircraft operators would migrate to airports where the approaches were not so weather dependant and not so demanding of resources.

16 January 2013






A CAA document from 2001 states:

Most current aircraft are designed around current PANS OPS 3 degree
approaches and are not certified to fly at angles greater than 3 degrees in CAT II or III
conditions. Further arrivals noise reductions would be possible in the future if new
aircraft were designed to permit a steeper approach gradient. Approaches steeper
than 3 degrees might provide a noise benefit by placing aircraft higher at any given
point on the approach, but raise potential difficulties in terms of certification of
approaches, particularly in low visibility. Because of these factors this Working Group
concluded that approaches steeper than 3 degrees are unlikely in the near to
medium term at Heathrow, Gatwick and Stansted.