1.5 Minimum Aircraft System Performance Specification 1.5.1 In addition to having the capability to maintain high levels of horizontal navigation accuracy it is essential that aircraft are also able to achieve a high standard of vertical navigation performance, particularly at RVSM designated levels within the NAT Region. At a technical airworthiness level, this is achieved by compliance with the altimetry MASPS which, amongst other things, specify requirements fora maximum value of Altimetry System Error (ASE) for two independent altimetry systems comprising an altitude alerting system and an automatic altitude control system. The MASPS were formulated in close liaison with the manufacturers of avionics equipment all new commercial aircraft types capable of operating at/or above FL 290 areas a general rule, built to a technical standard that complies with the requirements of the MASPS. For aircraft not compliant at manufacture, service bulletins have been produced by the manufacturers and approved by the appropriate certifying authorities.
