Airlines involved in two crashes reportedly declined to purchase extra safety equipment

Ethiopian Airlines and Lion Air in Indonesia reportedly declined to buy two add-on safety devices that might have helped the pilots keep the doomed Boeing 737 MAX jets in the sky.

Neither airline paid extra to have Boeing install the devices to have the "angle-of-attack" system display the readings of two sensors or for a "disagree light", which is activated if the sensors produce conflicting readings, according to news reports, which said both airlines may have declined to purchase the devices to keep costs down.

Boeing will install the equipment in all planes now being built and will retrofit MAX aircraft now in service, the company announced on Thursday.

Neither option was mandated by the US Federal Aviation Administration (FAA), The New York Times reported on Thursday.

The crash of Ethiopian Airlines' and Lion Air's Boeing 737 MAX jetliners five months apart led 42 countries worldwide, including China, to ground the aircraft. The US was the last major country to order the planes grounded. Investigators still do not know why the Ethiopian and Indonesian jets crashed.

The crashes raised questions about the jet's anti-stall device and how the planes were certified as safe. Boeing is cooperating with the investigation and is eager to determine the cause of the crash and resolve the issue, assuming the planes did not crash due to pilot error.

The Ethiopian Airlines crash killed all 157 people aboard. The Lion Air crash killed all 189 people aboard.

The Ethiopian Airlines pilot did not train on a simulator before flying the MAX jet, according to The New York Times. Use of a simulator is generally considered essential training before piloting a new type of aircraft, even the 737 MAX, an updated version of prior Boeing planes.

Both planes flew erratically after experiencing difficulty with the Maneuvering Characteristics Augmentation System (MACS), the anti-stall device.

An "angle of attack" sensor built into the aircraft measurers the amount of lift produced by the wings. The device warns pilots when there is too little lift, potentially stalling the plane, and then points the nose of the craft down to gain speed and remain aloft.

The three US airlines flying the Boeing 737 MAX tailored the new planes to fit their operational needs.

American Airlines, which purchased 100 737 MAX planes and currently has 24 in its fleet, purchased both the "angle of attack" indicator and the "disagree light", the company said.

Southwest Airlines, which ordered 280 of the planes and has 36 in service, purchased the "disagree light" alert option and installed an "angle of attack" indicator above the flight crew's heads.

Following the two fatal crashes, Southwest said it will modify the controls to display the "angle of attack" indicator on the pilot and co-pilot's main computer screens.

United Airlines, which ordered 137 Boeing MAX jets and has taken delivery of 14, did not order the indicators or disagree light. The airline said the crew uses other data to assure safety while in the air.

The US Transportation Department's inspector general, Calvin Scovel III, will testify next week before a Senate panel about questions surrounding the crash.

Daniel Elwell, acting administrator of the FAA, and Robert Sumwalt, chairman of the National Transportation Safety Board (NTSB), also will testify.

The FAA, which certifies aircraft as safe and operates the nation's civilian air traffic control system, is part of the Transportation Department. The NTSB investigates the cause of air, railroad and marine accidents.

On Wednesday, The Seattle Times reported that the FBI, the nation's top criminal investigative body for federal matters, will join other agencies in reviewing the certification of the Boeing MAX 737. The FBI declined to confirm the report, saying that it neither confirms nor denies what it may or may not be investigating.

Investigators at the US Justice Department are also reviewing the FAA's role in certifying the aircraft. CNN said Wednesday that the department has issued multiple subpoenas to Boeing and appears to be looking into how the MAX was certified and marketed.

The Pentagon said its inspector general plans to investigate a complaint that Patrick Shannon, acting US defense secretary and a former Boeing executive, violated ethics rules by allegedly promoting Boeing while in office. Shannon said he welcomed the investigation.