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ILS replacement

Updated 9 March 2017

Work to replace Heathrow’s landing systems is now due to finish on Friday 10th March, a day later than expected. This is because the safety flight checks required to test the new system were not completed last night due to poor weather conditions. This means these flights will need to be completed tonight.


We are replacing Heathrow’s landing systems – known as the Instrument Landing Systems (ILS). The ILS is a radio beam used to guide aircraft into land at Heathrow. There are four landing systems at Heathrow – one at each end of the two runways. These systems have come to the end of their life and need upgrading. The landing systems for the two westerly runways (known as 27L and 27R) have been replaced, along with the system for one of the easterly runways. This means we have one left to complete (runway 09L).

Work to replace the ILS for the northern runway (09L) which is used for arrivals during periods of easterly operations (i.e. when there are easterly winds) began on Saturday 4th March.

We have made every effort to minimise the impact on local communities by carrying out the work when a period of westerly operations is forecast (i.e. when there are westerly winds). This means there should be no impact to normal operations until the final day of works. However, on the final day (currently expected to be Friday 10th March) our normal runway alternation programme will be suspended. Aircraft will have to use the southern runway (27L) as the main arrivals runway all day (rather than alternating at 3pm as normal) and departing aircraft will have to use the northern runway (27R). This will mean that some residents will experience more overflights than usual on this day.

Although we are doing everything to ensure this work takes place during westerly operations, there is always a risk that the weather may change and we have to operate on easterly operations. If this occurs then we will need to use the southern runway (09R) for arrivals and the northern runway (09L) for departures, which will mean that some residents will experience more overflights than usual. We have selected the best window for the appropriate weather conditions to avoid this situation as much as possible.

Flight checks

In order to test the new landing system once it has been installed, safety flight checks are also required by the CAA. The checks are carried out by a small/light aircraft and involve the aircraft performing a number of approaches to test the new system.

These calibration flights take place during the night period when there are no other aircraft landing or taking off at Heathrow. The checks started on Tuesday 7th March and should be completed on Thursday 9th March. Because the aircraft is small we hope that there will be minimal disruption to residents.

We are very sorry for any disruption these works may cause. However, we hope you will appreciate that the work is essential to the safety of Heathrow’s operation.

More information about this can be found in the Q&A.