Franco-Italian turboprop maker ATR is tackling a slump in deliveries resulting from a combination of industrial delays, unsold aircraft and pilot shortages, which could particularly upset the plans of IndiGo to grow on underserved, smaller routes in India.

In India, a top growth market, ATR is struggling to deliver planes as quickly as it had hoped, partly due to problems finding enough pilots for leading customer IndiGo.

ATR agreed in 2017 to sell 50 ATR 72-600 aircraft, worth more than $1.3 billion at list prices, to the budget carrier, also India’s largest.

In order to grab one of the turboprop sector's biggest deals, ATR assumed responsibility for recruiting some pilots and instructors for IndiGo, which like many Indian airlines faces an acute shortage, sources told Reuters.

"The Indigo deliveries progress on a monthly basis," the spokeswoman said. "In addition, we are working with Indigo to address the pilot shortage and co-operate very closely with them on pilot instructors," she added.

IndiGo was not immediately available for comment.

The turboprop maker, owned jointly by Airbus and Italy's Leonardo, has delivered only a handful of aircraft in 2019 but aims to recover in the second half, industry sources said.

Toulouse-based ATR declined to give a figure for mid-year deliveries but said it was confident of achieving its target of matching last year's total handover of 76 aircraft.

The delivery snag is the latest indication of the cost of a global pilot shortage as air travel grows faster than the economy. In India, trained captains are particularly scarce.

ATR predicts annual average growth of 10.9 percent in 50-70-seat turboprop traffic in South Asia.

Deliveries can have an impact on revenue and profits as airlines pay most of the cost of a plane on delivery. Analysts say ATR is a useful source of additional profit for Airbus and Leonardo though its margins are not published.