been upgraded to "Stage 4" noise certification resulting in quieter aircraft. This has resulted in lower noise exposures in spite of increased traffic growth and popularity. In the 1980s the U.S. Congress authorized the FAA to devise programs to insulate homes near airports. While this does not address the external noise, the program has been effective for residential interiors. Some of the first airports at which the technology was applied were San Francisco International Airport and San Jose International Airport in California. A computer model is used which simulates the effects of aircraft noise upon building structures. Variations of aircraft type, flight patterns and local meteorology can be studied. Then the benefits of building retrofit strategies such as roof upgrading, window glazing improvement, fireplace baffling, caulking construction seams can be evaluated. Regulation Stages are defined in the US Code of Federal Regulations (CFR) Title 14 Part 36. For civil jet aircraft, the US FAA Stage 1 is the loudest and Stage 4 is quieter. Stage 3 was required for all large jet and turboprop aircraft at US civilian airports from the year 2000, and at least Stage 2 for under MTOW jets until December 31, 2015. The previous was Stage 4 for large airplanes, equivalent to the ICAO Annex 16, Volume 1 Chapter 4 standards, while the more stringent Chapter 14 became effective July 14, 2014, and was adopted by the FAA as Stage 5 from January 14, 2016, effective for new type certificates from December 31, 2017, or December 31, 2020 depending on weight. The US allows both the louder Stage 1 and quiet Stage 2 helicopters. The quietest Stage 3 helicopter noise standard became effective on May 5, 2014, and are consistent with ICAO Chapter 8 and Chapter 11. Night flying restrictions At Heathrow, Gatwick and Stansted airports in London, UK and Frankfurt Airport in Germany, night flying restrictions apply to reduce noise exposure at night. Satellite-based navigation systems A series of trials were undertaken at London's Heathrow Airport, between December 2013 and November 2014, as part of the UK's "Future Airspace Strategy", and the Europe-wide "Single European Sky" modernisation project. The trials demonstrated that using satellite-based navigation systems it was possible to offer noise relief to more surrounding communities, although this led to a significant unexpected rise in noise complaints (61,650 ) due to the concentrated flight paths. The study found that steeper angles for take-off and