Why are take-offs delayed at Mumbai airport?

Why are take-offs delayed at Mumbai airport?

Why do wait times at Mumbai airport for aircraft to taxi and take off increase as the day progresses? TOI uncovers a complex set of reasons, going beyond messages of simple ATC delays and congestion one hears onboard delayed flights.

No parallel taxiwaysApart from runway constraints, CSMIA lacks parallel taxiways. “The lone taxiway is a bottleneck. Aircraft coming from the eastern and western piers, and T1 (domestic terminal), all converge here, slowing the process of sending aircraft for line-up,” said a person in the know. A parallel taxiway is coming up but is only half-ready as a rescue and firefighting building in the middle of the path needs to be shifted. “Once a new casualty centre is ready in a month, MIAL will demolish the building that is posing a hurdle. The demolition and preparing the taxiway after that will take 18 months,” he said.

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Delayed ATC automation

“ATC’s arrival process is automated, but not the departure process… A lot of departure planning is based on human cognitive intelligence of the controller,” said a stakeholder. Automation is expected to be completed in the next few months. Air traffic controllers use targeted off blocks time (TOBT) derived under airport collaborative decision making (ACDM) to calculate start time for aircraft. Airlines are supposed to declare TOBT, but many don’t update it. “A flight may not be ready for departure but the same is not always conveyed to the controller. So its startup time remains the same while TOBT goes past that… Controllers thus have the superhuman task of juggling departure sequences at the last minute,” said sources.

Delayed flights

“Sixty-five per cent of inbound aircraft to CSMIA has been delayed in the recent past,” said a person in the know. The reasons include inflated block time where airlines show way more than the actual journey time for a route to boast of before-time arrivals. But this leads to discrepancy in slots with an airport expecting a flight at, say 3pm, and it arriving at 2.45pm. Earlier this month, aviation ministry reduced number of flights at CSMIA by about 40 after finding that MIAL did not “proactively” act on the issue of “excessive slot distribution”. The government said CSMIA “suffers from congestion and excess capacity on its runways which inadvertently leads to air space congestion, where flights are forced to hover over the city for 40-60 minutes.”

Progressive delays

“The OTP of morning departures is close to 85% on aircraft parked overnight. As the day progresses, this starts dropping. Mumbai is a hub airport with a lot of transfers. Airlines fly in crew to operate flights from other bases on other flights. A delay in these factors, apart from delayed arrivals, means that if there is a bunch of late arrivals, the controller’s planning goes for a toss. Then everything has to be replanned,” an official said. Delays begin when planes have to fly into Mumbai and then fly out. The accumulated delays progressively worsen during the day.

“Slot allocation in Mumbai did not factor in things like go-arounds, foreign object on runway or other things that inevitably and inadvertently happen, eating into hourly capacity. You can’t have peak runway hour usage 24×7. There has to be two hours of peak use followed by two hours with slightly less capacity to factor in those things. Govt move to cut flights was the right step. Air traffic controllers are doing a superhuman job at this constrained airport,” said a senior ATC official. “Holding planes in air means more fuel burn. Waiting on ground with engines off means not burning fuel. So we let planes wait on ground rather than in the air,” said a source.

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The net resultAll these handicaps have come to bite, given the boom in air traffic. While Mumbai airport was handling 970-980 aircraft daily before the order to cut flights, there were days when it consistently saw 1,000 flights with a combined passenger load of 1.6 lakh. Post-cuts, it handles about 950 flights daily. Still, the cascading delays don’t show any sign of going away. For instance, 72 flights which were to operate on Feb 25 (both arrivals and departures) operated in the early hours of Feb 26.

The solution

Navi Mumbai International Airport is still over a year away from opening its first terminal, till which time CSMIA will remain the only aerial gateway to India’s financial capital. To handle traffic effectively, experts say there is an urgent need to: expedite automation; improve on-time performance of airlines, especially of arrivals from tier two and three cities; bring slots closer to actual capacity that factors in unforeseen but inevitable events like go-arounds or runway being shut down for a while to remove foreign objects; adherence to airport collaborative decision making; infrastructure upgrade by MIAL; more efficient use of airspace. “AAI is upgrading integrated tower work position. Electronic flights strips are coming. MIAL is taking some interim steps like adding five-tug relief points (planes being disengaged from tug after pushback),” said a source. AAI has analysed the situation to tackle the issue of airspace congestion in Mumbai and cut flights after finding “persistent congestion” caused by excessive slot distribution with limited time margins by the airport operator, non-adherence of slots by airlines and non-scheduled operations during peak hours. “This action,” as per a govt statement issued on Feb 13, “has been taken in the larger public interest from the perspective of airspace safety, efficiency of operations and passenger satisfaction.”

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