N26906

HISTORY OF FLIGHT

On October 10, 2014 about 1300 UTC, a N26906, Boeing 787-824 operated by United Airlines (UA) as a 14 Code of Federal Regulations, Part 121 international flight from London's Heathrow International Airport (LHR), United Kingdom, to Houston's International Airport (IAH), Houston, Texas, was struck by lightning and three of five primary display units went blank, a status message related to a power distribution channel was displayed, and the captain's forward windshield heat became inoperative. The standby instruments and the heads up displays (HUD) were unaffected by the event. The lightning strike occurred approximately six minutes after take-off during the climb portion of the flight.

There was no checklist for a partial loss of displays and the crew elected to use the checklist for "Loss of All Displays". The procedure did not recover use of any of the three failed displays. The crew accomplished the abnormal checklist for the window heat. The checklist did not restore the function of the window heat. The remaining two displays were reconfigured and the flight crew landed the airplane uneventfully at LHR. There were no injuries to the crew and passengers. After landing, LHR maintenance performed a lightning inspection and found external nonstructural damage in five locations along the nose which was addressed in accordance with structural repair manual (SRM) allowable damage criteria. A power reset to the aircraft per maintenance manual procedures was accomplished, and the displays and other affected systems returned to normal function. After a review by United maintenance personnel, the aircraft was approved for dispatch and continued the flight to IAH with no further faults noted.

INJURIES

No injuries to passengers or crew were reported.

DAMAGE TO AIRPLANE

An on-site examination of the aircraft was performed while on the ground at LHR and the aircraft display systems were restored using aircraft maintenance manual (AMM) procedures. An external inspection of the aircraft by UA maintenance personnel revealed possible lightning strike attachment points on the left hand side of the nose of the aircraft. Damage was noted around the captain's windshield (L1) in the area of the seals of the windscreen. A review of maintenance records revealed that approximately one month prior to the event, window seal damage was noted in the same area of the L1 windows and was previously repaired. An additional set of possible lightning attachment points were documented on the left wing in the area of the left outboard aileron. The damaged areas were inspected by UA maintenance.

The aircraft was approved for dispatch in accordance with structural repair manual (SRM) allowable damage criteria. The flight continued from LHR to IAH without any other incidents.

An additional aircraft examination was conducted in March 2015. The interior of the nose area of the forward equipment bay in the location of the lightning strike points was inspected. The left side cockpit windows were visually inspected for signs of delamination of damage from the cockpit. No notable signs of additional damage were seen in the area of the lightning strike points or on the left side cockpit windows. A display unit and forward instrument panel electrical ground bonding check was performed finding all grounds satisfactory.

Three displays, the left inboard, left outboard and right outboard displays blanked during the event. The aircraft health monitoring system (AHM) noted faults related to the three display units, the left forward window heat system and the secondary power distribution system related to the left forward window heat system. After the flight's return to LHR, United maintenance performed an aircraft inspection and aircraft power reset per aircraft maintenance manual procedures and the displays and window heat system resumed normal functionality.

AIRCRAFT INFORMATION

The event airplane, a Boeing 787-824, serial number 34829, was manufactured and delivered to the operator in October, 2012 and had accumulated 6,582 hours and 996 cycles. The left inboard and outboard displays were delivered new with the aircraft. The right outboard display was installed in the aircraft in December 2012 to replace a unit that was removed due to erroneous display switching without crew input. None of the affected display units had been returned to the display manufacturer since the time of delivery of the aircraft.

METEOROLOGICAL INFORMATION

The crew reported the aircraft was flying through a "moderate non-CB (Cumulonimbus) rain shower" with cloud tops of 10,000 ft. at the time of the lightning strike.

FLIGHT RECORDERS

The aircraft was equipped with an Enhanced Airborne Flight Recorder (EAFR). The data from the EAFR was successfully retrieved and sent to NTSB for analysis.

TEST AND RESEARCH

Aircraft Level Grounding/Bonding Test

In March 2015, a grounding/bonding test was performed on the event aircraft. Bonding checks were performed on the head down displays and the P300 and P400 electrical panels. The bonding measurements were consistent with bonding measurements from an exemplar aircraft. A visual inspection was also conducted and confirmed that the grounding straps between the forward instrument panel and the bulkhead on both the captain's and first officer's side were attached and secured.

Component Level Testing

The left and right inboard and outboard display units (DU), Secondary Power Distribution Unit (SPDU) microprocessor card, Graphics Generator Module (GGM) and Window Heat Protection Unit (WHPU) were removed from the event aircraft for additional testing and inspections. The details of the testing and inspections can be found in the NTSB Systems Group Chairman's Factual Report contained in the public docket for this incident.

Additional fault history data was recovered from the non-volatile memory on the Secondary Power Distribution Unit (SPDU) microprocessor card, Graphics Generator Module (GGM) and the four removed display units (DU). A review of the DU fault history data showed that the display units that blanked all recorded a "LCD Supply Voltage Fault" at the approximate time of the lightning strike as reported by the crew.

The right inboard and outboard units were subjected to the manufacturer's acceptance test procedures (ATP) and return to service (RTS) test procedures. Both units passed both the ATP and RTS test procedures. The left outboard unit was selected to be used for additional testing and the left inboard unit was quarantined as a control unit.

Exemplar Unit Testing

Testing on an exemplar display unit was performed by the component manufacturer. The exemplar unit was equivalent to the event units except for the display software. The software in the exemplar display was modified to add additional internal fault reporting output, but was otherwise equivalent to the event units.

The testing consisted of both radiated field and cable coupling tests, in both grounded and floating conditions (when applicable) for the display. The different test conditions the exemplar display was subjected to and all the test levels exceeded or were outside of 787 display specifications. During the exemplar unit testing, the display did not have any adverse effects or fault messages logged that were directly related to the effects or messages seen during the event.

Near Strike Lightning Testing

Additional testing was identified that addressed radiated electric fields that are coupled directly into the equipment. The purpose of the testing was to evaluate the susceptibility of a 787 DU when exposed to a high intensity electric field radiated inside the cockpit generated by a nearby lightning strike. The testing did not look at magnetic field effects. The testing was based on standardized system level testing as described in MIL-STD-464C and was not required to be conducted for display unit or aircraft certification.

The testing was conducted at the aircraft manufacturer's lightning laboratory. Testing was conducted on both an exemplar DU and the event airplane's left outboard DU. Nine near lightning strikes were performed on the exemplar unit with one strike resulting in a blanking event on the display. A review of the NVM fault data for the display showed a "Grayscale voltage fault" was logged by the unit.

The left outboard unit from the event aircraft was tested. Four near lightning, two in a near vertical (approximately 19° from vertical) orientation and two in a horizontal orientation were performed. Blanking of the display was observed in one of the vertical and both of the horizontal tests. Each test that resulted in blanking resulted in a "LCD Supply Voltage Fault" logged by the display unit.

Flat Plate Testing

Based on the results from the near strike lightning testing, additional testing using a flat plate to create a transient electric field across the display surface was performed at the display manufacturer. The testing that was performed was not required to be conducted for display unit or aircraft certification. The testing was performed on the exemplar display and the left inboard, right onboard and outboard display units. A charge would be applied to the flat plate placed on a Lexan sheet resting on the display unit. Once the appropriate charge level was achieved the plate was rapidly discharged and the display behavior was observed. All four units, experience blanking at different applied voltages and recorded both "Grayscale voltage fault" and "LCD Supply Voltage Fault" during the blanking events.

ADDITIONAL INFORMATION

Electrical Field Analysis

Based on the results from both the near strike lightning testing and the flat plate testing, the Boeing Company conducted an analysis of the electrical fields present in the cockpit during a lightning event.

The analysis used three current waveforms ("A", "D" and "H"), from ARP 5412 revi...