SHANGHAI (Reuters) - China’s domestically developed C919 passenger jet completed its second test flight on Thursday, the jet’s maker said, but the duration and near five-month gap since its first flight have raised questions over whether its latest delivery target can be met.

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The narrow-body C919, which will compete with Boeing Co's BA.N 737 and the Airbus SE AIR.PA A320, is a symbol of China's ambition to muscle into a global jet market estimated to be worth $2 trillion over the next 20 years.

However, the program has faced lengthy delays and missed its original target of delivery to customers by 2016 - a date reportedly pushed back to 2020. Sales to date have been restricted largely to its home market because it has yet to be certified by regulators in the United States and Europe.

Thursday’s flight was the second for the initial C919 test model, whose maiden flight was on May 5. The second of six planned test aircraft, which achieved power-on of its systems in July, has yet to fly.

Commercial Aircraft Corp of China Ltd (COMAC) [CMAFC.UL] said the plane reached an altitude of 10,000 feet during a flight that took off from Shanghai’s Pudong Airport at 07:22 a.m. (2322 GMT) and landed at 10:08 a.m.

“Various elements of the test flight, including with the raising/lowering of the landing gear, were all completed smoothly,” COMAC said in a statement.

The 166-minute flight time was more than double the maiden flight of 80 minutes, but 54 minutes shorter than plans detailed in an article published by state-backed news website ThePaper.cn earlier on Thursday. COMAC did not immediately reply to questions from Reuters on whether the flight was shorter than planned.

Bradley Perrett, a veteran China watcher and reporter at Aviation Week, said the five-month interval between the aircraft’s two flights was “extraordinary” and COMAC’s reported delivery target of 2020 appeared not to be firm.

“The conclusion must be that COMAC was not really ready for flight testing in May,” Perrett said in an article published on Wednesday. “A common view is that the C919 was put into the air so early for strictly political reasons, although there is no suggestion that doing so was unsafe.”

Mitsubishi Heavy Industry Industries Ltd's 7011.T, Mitsubishi Regional Jet - Japan's first passenger aircraft - took its second flight eight days after it first flew in 2015 while the gap between the first and second flight for the Airbus A350 was five days, Perrett said.

Strongly backed by China’s government, COMAC has so far announced orders for 730 C919 planes from 27 customers, many of which are Chinese leasing companies.

Though billed as homemade, the C919 relies on overseas technology from firms including General Electric Co GE.N, France's Safran SA SAF.PA, Honeywell International Inc HON.N and United Technologies Corp UTX.N.

COMAC also said its ARJ21 regional jet was in the air at the same time as the C919 on Thursday, marking the first time two types of domestically made passenger jets have taken to China’s skies simultaneously.