* Biggest aircraft investment by a Greek carrier
* One of largest Greek investments since debt crisis
* 30 Airbus planes on firm order, option for 12 more (Adds Aegean CEO, Airbus executive comments, details)
By George Georgiopoulos
ATHENS, March 28 (Reuters) - Greece's largest carrier Aegean Airlines picked Airbus for an order of 42 aircraft worth $5 billion (4 billion euros) to renew its fleet of single-aisle planes and add capacity for future expansion, executives said on Wednesday.
The order is the largest by a Greek carrier and one of the biggest investments by a private Greek company since the country's debt crisis erupted in 2010.
Seeking to reduce maintenance costs, Aegean, a member of the Star Alliance airline group, had been considering the Airbus A320neo or Boeing's 737 MAX, with its people working on the project for the last 12 months.
"Today is a very important day for Aegean," Vice-Chairman Eftychios Vassilakis said during a news conference. "We confirmed our commitment to improve our competitiveness by signing a deal for an order of up to 42 aircraft."
It is the third time in 19 years that the carrier is investing in new airplanes, Vassilakis said, "aiming to offer our passengers the newest and most technologically advanced planes as we remain focused on quality."
Aegean signed a Memorandum of Understanding with Airbus. It said the agreement included a firm order of 30 aircraft from the A320neo family, with an option of 12 additional jets with new generation engines offering fuel savings of 15 percent.
The agreement was part of a fleet expansion and renewal programme expected to take place between 2020 and 2025, Aegean said.
Ten of the 30 jetliners in the firm order will be Airbus A321 neo aircraft - which are part of the A320 family of planes - while the remaining 20 would be the slightly smaller A320 neo jets, an Airbus executive said.
"Airbus offers a choice of powerplant between CFM Leap and Pratt and Whitney engines," the executive told Reuters, declining to be named. "Boeing's 737 Max planes come only with CFM Leap engines."
Aegean's CEO said the carrier would decide on the type of engine and the mix of planes at a later stage.
"The new airplanes are just the hardware," said Aegean's CEO Dimitris Gerogiannis. "It is our people who make the difference, not the metal."
Aegean, which flies domestic and international routes, also owns former flag carrier Olympic Airlines, which was privatised in 2013. Most of its current leases need to be replaced between 2019 and 2023.
Last year, Aegean grew full-year net earnings by 87 percent on an improved load factor and higher sales, riding a strong tourism year. In 2017 it flew a total of 13.2 million passengers.
1 euro = $1.2387 Reporting by George Georgiopoulos Editing by Jason Neely and Jane Merriman