Two Maintenance Mistakes Reveal Similar Systemic Shortcomings

Air Safety Week, March 15, 2004

A Lufthansa [DLAKY] jet whose wingtip came within five feet (1.6 meters) of striking the runway during takeoff shows that high technology fly-by-wire aircraft can be as vulnerable to maintenance error as aircraft of an earlier era with cable and pulley flight controls.

Two cases embody the same system shortcomings in government oversight, operator oversight of outsourced maintenance, clarity of the maintenance manuals, and functional checks of critical flight controls following maintenance. The fly-by-wire jet involved an Airbus A320, in which the captain's side-stick controller had mistakenly been cross-wired during maintenance (see ASW, June 4, 2001).

The cable and pulley aircraft involved a tailheavy Air Midwest twinturboprop that pitched up and crashed on takeoff, killing all 21 aboard. Due to incorrect rigging of the control cable, elevator movement of the Beech 1900D was restricted by about half, leaving the doomed pilots with insufficient control authority to save the situation.

In its investigation of the fatal Jan. 8, 2003, crash at Charlotte, N.C., the National Transportation Safety Board (NTSB) pointed to maintenance deficiencies extending from the shop floor up to carrier and government oversight (see ASW, March 1).

The 121 passengers and crew of the Lufthansa jet were more fortunate. In this case, despite an undetected maintenance error, one feature of the incident airplane's fly-by-wire technology helped the pilots to save the situation. A control button enabled the first officer to override the captain's malfunctioning sidestick, level the wings, and climb the airplane to a safe altitude. It was a very close call.

For an aircraft on takeoff power, and a wingtip a mere 1.6 meters above the ground, a few fractions of an inch of additional false sidestick input by the captain could have caused the airplane to slam into the ground. In its investigation of the March 20, 2001, takeoff incident at Frankfurt, the German Federal Bureau of Aircraft Accidents Investigation, the Bundesstelle fur Flugunfalluntersuchung (BFU), found many of the same systemic problems in maintenance that the NTSB uncovered in the Air Midwest crash. The English language version of the BFU report was just recently released.

The similar findings in these two cases, involving airplanes representing two different generations of technology, continents apart, operating in countries with well-established regulatory bodies, suggest that maintenance shortcomings may be global threat to air safety.

The Lufthansa jet had just come out of maintenance at the Lufthansa Technik AG facility at Frankfurt. The airplane had gone into maintenance because of reported in-service problems with the No. 2 elevator aileron computer (ELAC). Lufthansa Technik performs maintenance for Lufthansa German Airlines. The two are separate corporate entities.

In trouble-shooting the balky ELAC, technicians found a bent connection pin. Unable to fix the pin, they decided to replace the plug, which is one of four such plugs. A spare plug was not in stock. The technicians decided to reconnect all 420 connector pins to their associated wires, a complex job in "a most confined space" the BFU noted.

Two of the wires were connected backwards. The erroneous reconnection meant that the left (captain's) sidestick control was hooked up backwards. Pushing the sidestick to the right - for a right wing down command - would actually move the right wing up.

After the maintenance work was completed, the functional test was conducted on the first officer's (right side) sidestick only. It checked out properly.

The captain was the pilot flying during the airplane's first flight following this maintenance activity. To counter turbulence during takeoff, the captain applied right sidestick, which surprisingly brought the left wingtip down further, to an angle of some 21.4[degrees]. The alert first officer pushed the priority button, righted the airplane with his sidestick, and the aircraft climbed out. Leveling off at 12,000 feet, the planned flight to Paris now not likely, the pilots determined that the captain's sidestick was given control "outputs" that were opposite to the commanded "inputs."

They landed back at Frankfurt with the first officer flying, the airplane was returned to maintenance, and the BFU commenced its investigation.

The undetected maintenance error was cited as the probable cause of the near crash, but the contributing factors may be the more sobering bill of particulars. They parallel almost precisely the NTSB's findings in the Air Midwest case. The BFU cited:

* "Unclear and difficult" documentation so that a wrong wiring diagram was used.

* Diversion from the manufacturer's data by maintenance support.

* A manufacturer's maintenance manual that was not "formatted unambiguously."

* An incorrect functional check following completion of the maintenance.

* Lack of operator (Lufthansa) supervision of the maintenance organization (Lufthansa Technik).