Why do airlines ground planes? Where do broken airplanes go?

On Monday (October 7), India's largest aviation company, IndiGo, said that they have grounded around 30 aircraft due to "supply chain disruptions". 

To put it simply, these 30 flights were facing maintenance-related issues, and due to a disruption in the supply of the required engine parts, these flights were grounded. 

So when we say a plane is grounded, they are quite literally 'grounded'.  

Aeroplanes groundings are, however, rare case instances and can have a huge economic impact on the maker of the aircraft and on the airlines that fly them. 
It can however occur due to a few possible reasons:
 
1. When a plane gets old and retired: A plane cannot fly forever, hence after a point of time, they retire and are grounded.

But where? Cars that are too old to run are taken to scrapyards. Similarly, aircraft are sent to sites called boneyards or graveyards. There they are either kept for storage with some maintenance or have their parts removed for reuse or resale and are then scrapped. While some boneyards specialise in commercial aircraft, others are into defence aircraft. A few aircrafts are bought by or given away to museums or other educational institutions for display. 

Due to their extensive aircraft ownership, the United States has graveyards and boneyards smack dab in the middle of deserts. India doesn't have its own graveyard for planes.

What happens with Indian aircraft after they are retired?

In terms of civil aviation, the majority of the planes used by Indian airlines are leased. Once the lease period is complete, the lessors, who are often based overseas, take them back. In order to reuse the steel for their own or other organisations' needs, other fighter jets are melted down.

When Indian Air Force aircraft are retired, the organisation takes off all the avionics and equipment from it, and after adhering to the established laws and regulations, donates the aircraft to a museum for instructional purposes or some educational institutions.

2. Failures found during inspections: India's flight and aviation regulator, Directorate General of Civil Aviation (DGCA), recently tightened its inspection process. This was done when several incidents of technical glitches were reported with Spicejet.

Earlier, following 8 glitches in an 18-day period from June 19, DGCA conducted 53 spot checks on 48 SpiceJet planes between July 9 and July 13.

However, we should remember that when the Covid-19 pandemic was at its peak, it also became a reason for a lot of aircraft to get grounded.  

Current scenario in India: Aviation consultancy firm Corrective and Preventive Actions (CAPA) on November 1 said that more than 75 planes of the Indian carriers have been grounded due to maintenance and engine-related issues. These planes account for around 10-12 per cent of the Indian fleet.

If the issues with the aircraft are fixed, the plane can see the sky again. However, if it fails the inspections again, chances are they might be banned forever.