Amid rescue operations underway in Uttarakhand at the Silkyara tunnel site, a C-17 transport aircraft of the Indian Air Force has been deployed to airlift almost 22 tonnes of critical equipment from Indore to Dehradun, officials said on Friday.

Working round-the-clock with a powerful machine, rescue workers have drilled through up to 24 metres of rubble in the Silkyara tunnel till Friday afternoon, inching closer to the 40 labourers trapped inside for five days.

"The IAF has continued with its operations to assist the ongoing tunnel rescue underway at Dharasu, Uttarakhand. An IAF C-17 has been deployed to airlift almost 22 Tonnes of critical equipment from Indore to Dehradun. #FirstResponders #HADROps," the IAF posted on X.

It also shared images of the C-17 aircraft and a machine on-board in its post.

Meanwhile, sources in the IAF shared some of the challenges that were faced by the force on November 15 when it was pressed into action to assist in rescue operations undergoing near Uttarkashi in the hill state.

The rescue operations were "halted due to failure of an equipment" which was earlier utilised to create a passage, a source said.

The time-critical mission demanded a swift action to deliver the equipment as close as possible to the rescue location. The IAF took a prompt decision to launch its special operation platform C-130J -- Super Hercules -- to deliver the task, the sources said.

Dharasu ALG (Advanced Landing Ground), located at Chinyalisaur, was identified as the nearest possible location for expeditious operation. The ALG is located nearly 30 km from the rescue site. Dharasu ALG is a short and narrow airstrip of 3,600 ft situated at an elevation of 3,000 ft above mean sea level, they said.

The IAF utilised an "integrated approach handshake with civil administration and the BRO (Border Roads Organisation)".

An IAF helicopter was launched prior to the final mission to ascertain the feasibility of operations, the source said.

During earlier feasibility trial, Dharasu ALG was "made unfit for routine operations" by a C-130J aircraft. Therefore, a "fine professional call was required to operationalise the ALG for this operation keeping in mind the criticality of mission," the IAF sources said.

The helicopter operation was planned with a C-130J pilot on-board to assess obstructions and runway condition. Multiple approaches were flown by the helicopter to ensure that the most suitable call is taken before clearing the ALG for such critical operations, they said.

The entire mission hinged upon two critical aspects, viz., ALG fitness and success of operation. The ALG was cleared in a short period catering for operation of a large platform, the source said.

"Initial operationalisation involved a quick vegetation clearance which could have been detrimental for the aircraft operations. The IAF undertook three missions and airlifted 27.5 tonnes of critical rescue equipment into this short airstrip," the source added.

The mission was undertaken amid the challenges of reduced visibility conditions during departure, heavy-weight landing at short and narrow airstrip and offloading in constricted space. The offloading of critical material at such remote places was itself a huge challenge for operations. Dharasu ALG "did not have specialised equipment required for offloading from C130J aircraft," the sources said.

In one of the cargo offloading, "a mud ramp was created locally to avoid delay in subsequent rescue operations". The flying operations needed calculated approach and adequate risk mitigation to undertake this non-routine critical operation, they added.

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