Following a serious incident in 2012, the European Aviation Safety Agency (EASA) recommends airports to make sure runway-holding points do not interfere with ILS signals.
The serious incident happened at Hamburg, Germany on March 28, 2012. An Airbus A320 was on final approach when the Primary Flight Display (PFD) began displaying erroneous glidepath information. The aircraft descended below the glideslope while the PFD showed the airplane to be on the glideslope. The A320 descended even further below the glideslope, yet the PFD showed it to be almost one dot above the glideslope. A go around was initiated after which the aircraft landed safely. An investigation published early 2015 by the French BEA revealed that a Boeing 737 that was holding short on the taxiway was positioned in an area that was considered a critical zone near the glideslope antenna. The aircraft caused a disturbance in the glideslope signal, leading to erroneous information being displayed on the PFD of the approaching aircraft.
EASA recommends that:
(a) Aerodrome operators review the locations of established runway-holding positions, particularly at locations where runway-holding positions are established within critical areas of ILS signals, and ensure that they comply with the applicable provisions, and that relevant procedures for the protection of the ILS signals are contained in the aerodrome manual;
(b) ANS providers review their procedures for ILS approaches in order to ensure that they contain the unconditional requirement that ILS critical areas are kept clear during ILS approaches to avoid permanent infringements of these areas;
(c) NAAs take into account, during their safety oversight activities, the recommendations in (a) and (b) above.