With two pilots who faked their qualification already arrested and two more on the run, authorities believe there is an organised racket to provide fake documents to aspiring pilots.
As the issue found an echo in parliament, Delhi Police said two pilots -- Meenakshi Sehgal of IndoGo and Swaran Singh Talwar of MDLR -- were absconding.
The Directorate General of Civil Aviation (DGCA) meanwhile said it was conducting a thorough check of around 4,000 commercial pilot licences.
But an official told IANS that the problem may not be as serious as was being made out to be.
"I don't think it is rampant," a senior DGCA official told IANS. He added that a system was in place to track down offenders.
The scandal came to light when IndiGo pilot Parminer Kaur Gulati, 38, was arrested March 8 for allegedly obtaining the Airline Transport Pilot Licence using forged documents.
On Saturday, Delhi Police arrested Air India pilot J.K. Verma on charges of using a forged mark sheet to acquire a pilot licence.
Verma had been a co-pilot with Air India since 1989. "We have registered a case of forgery and endangering people life at risk," said Deputy Commissioner of Police Ashok Chand.
"We have been given more names by DGCA," Chand told IANS, referring to Sehgal and Talwar.
He said: "They are believed to have paid Rs.10-12 lakh each to touts (to get pilot licences). We are investigating."
The Crime Branch fears that someone in DGCA may be involved in the racket.
The issue of passenger safety was raised in the Rajya Sabha by Bharatiya Janata Party's Kalraj Mishra.
"The arrest of an Air India pilot ... is a matter of concern, and it shows the aviation department is not taking the issue seriously," Mishra said.