Due to this, over 120 domestic departures have been affected, airport sources said, adding, "by the time the work gets completed, airlines' on-time performances will go for a toss, as the main runway will remain unavailable between 9 am and 5 pm till February 7".
They further said, "In the past two days, every airline has experienced a delay of up to 30 minutes as all the take-offs are now taking place from the 09-end of the main Runway 09/27 due to the glide path relocation."
The Mumbai airport and the Airports Authority are changing the glide path angle at the main Runway (27) to 3 degrees from the present 3.3 degrees to meet international norms.
Glide path is an equipment that gives vertical guidance to a landing aircraft. The aircraft locks the signal and the descent angle from the glide path and starts descending. Its function is to bring the aircraft to a proper spot or touchdown zone on the runway. Three degrees is considered the optimum.
Mumbai airport authorities say the situation is unavoidable and all stakeholders, including aviation regulator DGCA, are taken into confidence prior to the commencement of the work.
"This is something which is unavoidable. But we have informed all the stakeholders and have also taken all the factors into consideration and chosen the best time of the year to keep the risks to the minimum," an airport official said.
The airport handles as many as 600 flights everyday. The ILS (instrumental landing system) of the main Runway 27 has a glide angle of 3.3 degrees instead of the conventional 3 degrees since its inception.
A higher glide angle has inherent operational disadvantages such as unsuitability for Cat-II and Cat-III and prevents pilots from maintaining the prescribed speed on the final approach, the official said.
But changing of the glide angle from 3.3 to 3 degrees requires relocation of the glide path hut and DME antenna to a new location which is 71 meters from the current location along with other complexities, he added.
"So, due to the complexities involved in the process, this work was so far not undertaken by the AAI. Now if the flight trial of the new procedures are found to be successful, we will have 3 degree ILS from February 7. So, the airport will not have ILS approach for runway 27 till that time," the spokesperson said.
This means that if visibility drops, all flights would land on the secondary runway or on the 09-end of the main runway, and this would lead to a 15-20 minutes delays.
The airport has two intersecting runways-- the 11,000 feet long main runway (O9/27) and the 9,500-meter long secondary (14/32).