Safety reasons impose a minimum vertical separation (in terms of feet ..or meters) between aircraft during the flight and the logic behind this statement should not be discussed.
However as the IFR traffic increased since more than 300% from 1970 up to now, what has been in the past discussed at the ICAO, was the very minimum vertical separation, matching with the current state of technological development, that could be kept by the aircraft in order to fly safely within a particular volume of airspace.
The RVSM is meant as the solution, which optimizes the airspace and the flight consumptions while minimizing delays and airspace restrictions.
RVSM allows the reduction of the vertical separation above flight level (FL) 290 (29000 feet) from the traditional 2000-ft minimum to 1000-ft minimum (304,8 mt).
As a consequence, aircraft fly more fuel optimum profiles, airspace capacity is increased and in-flight delays are reduced. All of this by providing six additional cruising levels between FL290 (8839,2 mt) and FL410 (41000 ft or 12496,8 mt).
The RVSM program was launched by the ICAO in 1982 with the very intent of doubling the airspace capacity, between FL290 and FL410 and providing more opportunities for (properly equipped) aircraft to operate at closer to the optimum flight levels, resulting in fuel economies.
Between 1997 and 2005 RVSM was implemented in all of Europe, North Africa, Southeast Asia, North America, South America, and over the North Atlantic, South Atlantic, and Pacific Oceans.
However, not all aircraft can fly in RVSM as it depends from the carriage and serviceability of specified aircraft equipment and the existence of appropriate operating procedures to ensure that the risk of loss of separation is no greater than it would be outside RVSM airspace.
The required aircraft equipment is the following: two independent altitude measurement systems, an altitude alerting system, an automatic altitude control system; and a secondary surveillance radar (SSR) transponder with altitude reporting system that can be connected to the altitude measurement system in use for altitude keeping.
Stringent regulatory requirements also ensure the RVSM reliability and safety but peculiar circumstances might still surprise the operators, even after so many years of RVSM experience.
It is in fact already well known that severe turbulence may affect the aircraft ability to maintain RVSM heigh requirement but it is not expected at all that wake vortex of an RVSM approved (although huge) aircraft may jeopardize the flight safety of another (relatively much smaller) RVSM approved aircraft.
The Challenger 604 lost about 10,000 feet until the crew was able to recover the aircraft, restart the engines and divert to the closest airport. The aircraft received damage beyond repair due to the G-forces, and was written off. (Here the source article).
Therefore we are now in an urgent need to increase the lateral separation between Airbus A380s and smaller aircraft.
EASA is expected to release a safety information bulletin soon with further guidance for controllers and pilots working on it (source).
A detailed report of the accident can be found here.
– Detailed accident report from the Aviation Herald
– Details on RVSM (skybrary.aero)
– Appendix G to Part 91 (ICAO)
– A380 wake flips Challenger 604 upside down
– Challenger 604 RVSM approved