“Silent Safety” would be the optimum solution if you asked habitants around an airport and pilots about their wishes on how approaches and departures should ideally be performed. Expanding the group of interviewees by Air Navigation Service Providers (ANSPs) and airlines, you would end up with “Silent and Efficient Safety”. But meeting all these three targets by 100 per cent is simply a utopian dream as aircraft operations are always somewhere between the edges of a “safety-sustainability-efficiency” triangle. Operational experience shows that balancing those three is rarely a win-win situation.
Recently operating into Frankfurt International Airport I found different Standard Departure Routes (SID) towards the intersection TOBAK. The TOBAK 4F/J SIDs have 21NM up to intersection TABUM, if you are assigned TOBAD 7N, the mileage is 45NM again up to intersection TABUM. These additional 24NM is an operational measure in order to mitigate aircraft noise. One can easily see that efficiency of a flight is heavily reduced while noise abatement, i.e. avoidance of overflying densely populated areas, is improved.
On the other sides of the triangle lie flight safety and noise abatement. Until 1972 it was standard to fly an Instrument Landing System (ILS)-approach fully configured, i.e. landing flaps fully set, landing gear down from about 10 NM distance from Threshold. The same year a group of technical experts developed the “low power/low drag” or “Frankfurter” Approach for approaches into Frankfurt Airport in an effort to reduce noise nuisance in the surrounding cities.
Forty years later, this type of approach, in which landing gear and flaps are extended later while the aircraft is descending at near idle-thrust is accepted as a common standard. Why? Because efficiency of flights and noise abatement is significantly improved while safety is not compromised on a standard approach featuring vertical guidance.
But even today, most airlines mandate configuring aircraft earlier for landing, thereby reducing efficiency and noise abatement, if there is no vertical guidance for the approach available. This could be the case if a traditional non-precision approach has to be flown in adverse weather situations.
During these types of non-precision approaches in adverse conditions the crew’s workload is increased to a point where safety would be reduced to an unacceptable level if crews would still be mandated to stick to “low power/low drag” procedures. In other words, priority is shifted from efficiency and environmental issues towards flight safety.
Constantly changing focus and shifting priorities is the way we operate every day. When safety is not compromised, environmental issues and/or flight efficiency are given the priority. But, and this is a large but, flight safety must never be compromised. This is reflected in the old saying “safety first”.
Looking at today’s developments, the essence of this saying may be scrutinized.
For example, the exponential growth of crosswind/tailwind take-offs and landings, despite being a less safe option, could be explained by environmental concerns and the industry’s constant capacity drive. Landing into the wind was accepted standard for long time as the aircraft simply flies because of the motion of the wind over the aerofoil. Thus landing into the wind reduces the speed over ground of an aircraft at touchdown. This in turn reduces demands on landing gear, engine and breaks, reduces landing distance needed and by that decreases chances of runway overruns. However, starting to let aircraft land in tailwind conditions because of environmental issues, we need to carefully assess the safety risks of these operations.
The same is true for restrictions of reverse thrust, a feature that can significantly increase deceleration rates and reduce landing distance – and thereby prevent runway excursions – or, in the event of a rejected take off, reduce stopping distance. Airlines usually train crews to omit use of reverse thrust for efficiency reasons. However, if reverse thrust is needed, it should be used.
Similarly, most airports also restrict the usage of reverse thrust – a policy which goes against the recommendations by EUROCONTROL’s European Action Plan on the prevention of Runway Excursions (EAPPRE). This restriction often results in a “discouraging” effect – reverse thrust is still used albeit at a later stage. This in turn reduces available safety margins greatly as reverse thrust is most efficient immediately after landing in high speed regime, as recommended by EAPPRE.
Generally speaking, every increase in flight efficiency or noise abatement is likely to entail a certain reduction in flight safety, regardless of whether we talk about tailwind landings, ineffective routings or steep approach descents. This is why pilots with an operational background are needed to evaluate the extent of this reduction in flight safety. Assessing the possible gains and drawbacks of new initiatives or technologies together with all stakeholders will certainly help us find the right balance between safety and efficiency.
Finally, it has to be said that no one is questioning the legitimacy of noise abatement or reducing the environmental footprint of aviation. Residents around an airport do have fully legitimate interests in quieter take-offs and landings. The same is valid for airlines and ANSPs - cutting down on congestion and delays-problems that ultimately lead to higher airline operating costs. But while reducing efficiency of flights it may cost a significant amount of money, reducing flight safety could cost a significant number of human lives.
It is our challenge today to balance these three basic needs while keeping flight safety as our collective number one priority.