FRANKFURT and WASHINGTON – The Ethiopian Airlines Boeing 737-8 that crashed shortly after takeoff from Addis Ababa March 10 did not have any known maintenance issues and was dispatched "clean" for its final flight, the airline's chief executive said hours after the accident that killed all 157 people onboard.

"From the records that we have, it was a clean airplane," Ethiopian Airlines CEO Tewolde GebreMariam said. "The routine maintenance checks didn't reveal any problems. I confirmed that it was a clean airplane."

The aircraft, operating as flight ET302 to Nairobi, departed Bole International Airport at 08:38 a.m. local time with 149 passengers and eight crew members onboard, the airline confirmed. Radar contact was lost at 08.44 a.m., six minutes after departure.

GebreMariam said the crew issued a distress call and requested a return to Addis Ababa shortly before contact was lost.

"From the air traffic control record, the pilot mentioned that he had difficulties and he wanted to return" to Addis Ababa, "so he was given clearance," GebreMariam said. "While it was in flight at around 08:44 a.m, [the aircraft] had difficulties and it was lost from radar," he said.

Flightradar24 data indicates the aircraft operated what appears to be a routine climb and acceleration for the first minute of its flight. The aircraft then leveled off at around 8,150 ft. before descending slightly. ET-AVJ reached a speed of close to 400 knots. Flightradar24 reports significant variation in vertical speed, although that data may be unreliable.

The Aviation Herald reports the last transponder data was received from position N9.027 E39.153 about 21 nm east of Addis Ababa. The aircraft was flying 8,173 ft., according to the website, terrain elevation in the region is 8,130 ft. Bole International Airport is at 7,625 ft.

The aircraft, ET-AVJ, arrived in Addis Ababa from Johannesburg at about 05:30 am March 10 after completing a routine scheduled flight—its third five-hour segment between the two cities within 24 hours. GebreMariam said the aircraft's records show no "technical remarks" following the last Johannesburg-Addis Ababa leg, and nothing was noted during its roughly three hours on the ground before its final departure.

On March 8, the aircraft was scheduled to operate flights 2861 and 2860 to Pointe Noire and back, but both services were canceled for an unknown reason. The aircraft remained on the ground in Addis Ababa.

The aircraft had its first “rigorous” maintenance check on Feb. 4, the airline said in a statement. "It was a brand-new airplane. Well-maintained," GebreMariam said.

Flight ET302's captain, Yared Getachew, had “more than” 8,000 flight hours and became a 737 captain in November 2017, the airline said. He joined Ethiopian in July 2010. “He has been flying with Ethiopian airlines with an excellent flying record,” GebreMariam said.

First officer Ahmed Nur Mohammed had 200 fight hours, the airline said.

"Ethiopian Airlines Group expresses its profound sorrow and deepest condolences to the families of the victims and their loved ones on the tragic plane accident," the airline said. "An investigation will be carried out to determine the cause of the accident, in collaboration with all stakeholders including the aircraft manufacturer Boeing, Ethiopian Civil Aviation Authority and other international entities. A committee comprising Ethiopian Airlines, Ethiopian Civil Aviation Authority and Ethiopian Transport Authority has been set up to carry out the investigations."

In a statement, Boeing said it was "deeply saddened" to learn of the accident. The company said it was standing ready to support the Ethiopian Airlines team. "A Boeing technical team is prepared to provide technical assistance at the request and under the direction of the U.S. National Transportation Safety Board (NTSB)," the company stated. NTSB is sending a team of four investigators to assist in the probe.

The aircraft involved was the airline's fourth 737-8 and was handed over on Nov. 15, 2018. The aircraft has been in service since Nov. 17, when it made its first revenue flight to Dubai. Flight ET302 was its first planned March 10 departure.

Ethiopian is one of the largest airlines in Africa and one of the few operating a hub connecting intra-African markets to its extensive long-haul network. In addition to the five 737-8s it already operated, the airline had placed an order for 25 more. The airline also has 13 Airbus A350-900s, two 787-9s, one 777F and 10 Bombardier Q400s on firm order, according to the Aviation Week Network Fleet Discovery database.

The airline operates 23 Boeing 737s, 10 A350s, five 767-300ERs, 19 777s (among them four -300ERs) and 22 787s.

The accident is the second of a 737-8 in just over four months. The first 737-8 accident took place on Oct. 29, 2018 near Jakarta, Indonesia. The aircraft, registered PK-LQP, had been delivered to Lion Air two months before the crash. All 189 people on board were killed when the aircraft impacted with the sea around 13 minutes after take-off. The Lion Air aircraft had a history of unreliable speed data input over the previous days but was retained in scheduled service after it had been cleared for operations by the airline’s maintenance division. The investigation is ongoing. One of the aspects being looked at is the Maneuvering Characteristics Augmentation System (MCAS) Boeing introduced on the MAX.

Ethiopian Airlines has been involved in three fatal accidents since 1996. A Boeing 767-200ER that had been hijacked ran out of fuel and was ditched into the sea near Mombasa/Kenya on Nov. 23, 1996, killing 125 of 175 people on board. On Jan. 25, 2010, Ethiopian flight 409, a Boeing 737-800, crashed into the Mediterranean shortly after take-off, killing all 90 on board. According to the accident report, pilots did not accurately control speed, altitude and heading, the aircraft stalled and control was lost.