A fighter aircraft on a test sortie, supposedly a Sukhoi-30 MKI, flew too fast and perhaps low enough to shatter Bengaluru’s midday peace on Tuesday.
At 1.20 p.m., people living in the east and south-eastern parts of Bengaluru, already harried by COVID-19 fears, were jolted by a deafening burst. Residents of almost half of the city reported on social media platforms that they felt tremors and rattling of windowpanes and objects at home for about 9 seconds.
Officials of the State disaster monitoring agency, KSNDMC, quickly dismissed initial fears of an earthquake.
After hours of confusing information, the mystery was somewhat cleared by the Indian Air Force, around 9.30 p.m.
Spokesman for the Ministry of Defence, Bengaluru, tweeted, “It was a routine IAF Test Flight involving a supersonic profile which took off from Bluru Airport and flew in the allotted airspace well outside City limits. The aircraft was of Aircraft Systems and Testing Establishment (ASTE) whose Test Pilots & Flight Test Engineers routinely test out all aeroplanes. The sonic boom was probably heard while the aircraft was decelerating from supersonic to subsonic speed between 36,000 and 40,000 feet altitude.
“The aircraft was far away from the city limits when this occurred. The sound of a sonic boom can be heard and felt by an observer even when the aircraft is flying as far away as 65 to 80 kilometres away from the person.”
Felt across many localities
The sound was heard as a boom, thunder, blast, and felt across Marathahalli, areas around the Hindustan Aeronautics Ltd. Whitefield, Electronics City, Fraser Town, Kammanahalli, Sarjapur, the football stadium, and Ulsoor in the east; Bannerghatta Road, M.G. Road, Jayanagar, and J.P. Nagar in the south, among other areas.
People in Anekal, 35 km away, and Malur, about 50 km away, also reportedly heard it.
The ASTE is located in the HAL belt at Marathahalli. Its experienced test pilots — who guarantee that a plane is safe to fly — routinely test-fly military aircraft that are under development, or every time a military aircraft is slightly tweaked, upgraded, serviced; or a device or part on the plane is added or replaced.
According to multiple unofficial sources, a Sukhoi-30 MKI fighter plane, probably being test flown by ASTE pilots, was flying over the city around the time. It may have gone supersonic — that is, breached the speed of sound (beyond Mach 1 or around 1,200 km per hour.) As the plane flies, depending on the height it flues at, the high speed creates a “sonic boom” or sound waves that ‘hit’ the areas below.
The present boom was one such, a former senior technical officer of the IAF said. If this sortie needed to test the speed or height, ideally it could have flown over fields around Bengaluru, the former IAF engineer said.
IAF’s Headquarters Training Command based in the city said in the evening, “No aircraft of training command was flying in the area. However, ASTE and HAL could have been undertaking their routine test flying, which necessitates going supersonic at times. These are done well beyond the city limits in specified sectors.”
It said, “However, considering the atmospheric conditions and reduced noise levels in the city during these times, the aircraft sound may become clearly audible even if it happened way out from the city.”
HAL spokesman Gopal Sutar said, “HAL aircraft or test flights have nothing to do with today’s sound in Bengaluru.”
Initially, a few residents suspected that a cooking gas cylinder may have exploded in the area. Another theory was that the burst was due to the build-up of cyclone Amphan in the Bay of Bengal.
Earlier in the day, Bengaluru Police Commissioner Bhaskar Rao said he had asked the Air Force Control Room if a plane had caused it.
Karnataka State Natural Disaster Monitoring Centre said, “The activity reported in Bengaluru is not due to an earthquake. The seismometers did not capture any ground vibrations as generally happens during a mild tremor. The activity is purely a loud unknown noise.”