New Delhi, July 5: The Qutb is quaking at the vibrations from the sky.

The new threat to the tallest tower in Delhi is from planes taking off from and landing at Indira Gandhi International Airport nearby.

The Archaeological Survey of India (ASI), in charge of the 12th century monument’s upkeep, has written to the Airports Authority of India (AAI) asking it to immediately change the flight paths that lead to the new third runway.

According to the ASI, the flights using this runway are flying “dangerously close” to the 234ft-high red sandstone monument.

“We have written to the airports authority explaining how the vibrations of the low-flying aircraft could endanger the Qutb, one of the biggest tourist attractions in Delhi,” ASI director K.K. Muhammed told The Telegraph.

The AAI, he said, has agreed to conduct a study to assess the impact of the vibrations on the tower, whose construction was started by Qutbuddin Aibak in 1173AD and finished by Iltutmish in 1200AD.

The problem is said to have started since September 2008, when the third runway was opened as part of plans to help the airport handle more traffic. One end of the new strip is about 2.5km closer to the Qutb than the old runways.

The ASI had raised similar concerns about plane vibrations to the 10th century temples in Khajuraho, a Unesco world heritage site, a few years back. The ASI had found the Nandi, Mahadev and Lakshman temples in the complex weakened by the vibrations.

Muhammed said the Madhya Pradesh government took serious note of the threat and approached the civil aviation ministry, which agreed to change the direction of an airstrip near the temple complex. He hoped a similar solution would be worked out for the Qutb.

This is not the monument’s only brush with danger. It has already tilted 25 inches — like the tower of Pisa in Italy — to the southwest.

It was in the danger of leaning further because of a weak foundation being further damaged by years of rainwater seepage. But the ASI partly solved the problem by cementing the area around the structure with lime to make it watertight. Six underground water cavities were dug up at a depth of 12ft to prevent water from reaching the 10ft-deep foundation of the structure.