AIRCRAFT SERIOUS INCIDENT REPORT EXECUTIVE SUMMARY

Section/division Accident and Incident Investigation Division Form Number: CA 12-12b AIRCRAFT SERIOUS INCIDENT REPORT EXECUTIVE SUMMARY Reference: CA18/3/2/1165 Aircraft registration ZS-ZWS Date of incident 13 March 2017 Time of incident 0933Z Type of aircraft Boeing 737-800 (Aeroplane) Type of operation Commercial (Part 121) Pilot-in-command licence type Airline Transport Age 45 Licence valid Yes Pilot-in-command flying experience Last point of departure Next point of intended landing Total flying hours 12 017.0 Hours on type 6 762.0 Port Elizabeth Aerodrome (FAPE), Eastern Cape OR Tambo International Aerodrome (FAOR), Gauteng Location of the incident site with reference to easily defined geographical points (GPS readings if possible) Near the IMGEV waypoint, 23 nm west of Warden, Free State (GPS position; 28 14 54 S 028 20 10 E) Meteorological information Number of people on board Synopsis Upper wind: 280 /36 kts, Temperature: ISA+6, Visibility: 10 km 2+4+130 No. of people injured 0 No. of people killed 0 On 13 March 2017, flight BA6234 (a Boeing 737-800) and flight SA8053 (an Embraer ERJ135) converged on waypoint IMGEV under radar control. SA8053 was at its cruising altitude of FL370 while BA6234 was cruising at FL410. Both aircraft were destined for OR Tambo International Airport (FAOR). Johannesburg Area South East cancelled BA6234 s Standard Arrival and instead routed the aircraft direct to waypoint ETLIG. This placed BA6234 too high for the flight management computer s vertical bearing. BA6234 was cleared to descend from FL410 to FL380. This was done at an increased vertical speed in order to capture the optimised vertical bearing. While on the descent, a traffic advisory was generated by the traffic collision avoidance system. This was followed immediately by a resolution advisory in both aircraft. Both crews complied with the resolution advisory. At the point of levelling off, BA6234 had exceeded its cleared altitude by approximately 500 ft. This meant that the safe clearance distance between both aircraft was 500 ft. and 1.6 nm. Once separation was regained, both aircraft continued on safely to their destination. Probable cause After BA6234 was rerouted direct to ETLIG, the flight management computer required a faster rate of descent in order to accomplish the planned vertical bearing for ETLIG. The crew began the descent from FL410 to FL380, but inadvertently (whether it was a human or machine error is unknown) descended through the assigned level before levelling off following a resolution advisory. SRP date 14 August 2018 Release date 21 August 2018 CA 12-12b 01 FEBRUARY 2017 Page 1 of 22

Section/division Accident and Incident Investigation Division Form Number: CA 12-12b AIRCRAFT SERIOUS INCIDENT REPORT Name of Owner Name of Operator Manufacturer Model Nationality Registration markings Place Date : 13 March 2017 Time : Comair Ltd / SA Airlink (Pty) Ltd : Comair Ltd / SA Airlink (Pty) Ltd : Boeing Aircraft Company / Embraer S.A. : 737-800 / EM-135-LR : South African : ZS-ZWS / ZS-SNX : En route from the southwest at waypoint IMGEV : 0933Z All times given in this report are Coordinated Universal Time (UTC) and will be denoted by (Z). South African Standard Time is UTC plus 2 hours. Purpose of the Investigation: In terms of Regulation 12.03.1 of the Civil Aviation Regulations (2011) the purpose of investigation of an aircraft accident or incident is to determine, in terms of the provisions of this Part, the facts of an accident or incident in the interest of the promotion of aviation safety and the reduction of the risk of aviation accidents or incidents, and not to establish blame or liability. Disclaimer: This report is produced without prejudice to the rights of the CAA, which are reserved. 1. FACTUAL INFORMATION 1.1 History of flight 1.1.1 At 0837Z on the morning of 13 March 2017, flight BA6234 took off from Port Elizabeth Aerodrome (FAPE), on a scheduled domestic passenger flight to OR Tambo International Aerodrome (FAOR). On board the aircraft were six crew members and one hundred and thirty passengers. The first officer (FO) was the pilot flying (PF). The aircraft was cleared to climb to its cruise altitude of flight level (FL) 410 while complying with reduced vertical separation minima (RVSM) flight rules. As the aircraft was approaching top of descent close to position IMGEV, the CA 12-12b 01 FEBRUARY 2017 Page 2 of 22

crew were cleared to descend from FL410 to FL380 by the area controller at Johannesburg Area South East on the VHF frequency 132,15 MHz. Descent commenced one minute and twenty seconds after the controller issued the clearance. Sometime after that, according to the pilot-in-command (PIC), they received a rerouting instruction to position ETLIG from the controller. This routing was entered into the aircraft flight management computer (FMC), whereupon the FMC recalculated a position that placed the aircraft too high on the descent profile, and therefore the FO initiated an increased rate of descent (ROD) to recapture the appropriate descent profile. As the crew continued with the descent the TCAS TA (traffic advisory) aural advisory warning was activated, which was followed almost immediately by a TCAS RA (Resolution Advisory) adjust vertical speed. The aural warning given in the cockpit could be heard during the radio transmission when the crew communicated with the controller at 09:31:40Z advising him of the RA. The FO then disconnected the autopilot and auto-throttle and followed the RA command by increasing the pitch attitude nose down. Moments later they received the ACAS clear of conflict call. The PIC then advised the controller that they were clear of conflict. The FO indicated that his focus was then on the pitch attitude and airspeed. He recalled that the altimeter showed 37600, and that the PIC called check altitude, whereupon he increased thrust and attitude to return to FL380. The flight continued normally to FAOR. 1.1.2 At 0912Z, flight SA8053 took off from Moshoeshoe International Aerodrome near Maseru in Lesotho (FXMM) on a scheduled international flight to OR Tambo International Aerodrome (FAOR) in South Africa. On board the aircraft were three crew members and sixteen passengers. The aircraft was cleared to climb to its cruise altitude of FL370. While maintaining cruise altitude the crew suddenly received a TCAS TA display in the cockpit. The PIC stated that he then put his hands on the controls in order to manoeuvre the aircraft should a TCAS RA occur. The FO then switched on the aircraft external lights as per standard operating procedures (SOP) in order to make the aircraft more visible. The crew then started to scan the area outside to try and visually identify the other aircraft. The TCAS displayed an amber TA indication showing an aircraft at a higher altitude, descending. At this stage the traffic display on the TCAS indicated a vertical separation of more than 1000 feet. As to what triggered the TCAS TA, the PIC thought it must have been the high ROD of the other traffic, as they were maintaining FL370. The next moment the crew visually identified the other traffic outside to their left. It was about this time that they reported a TCAS RA. The controller acknowledged the RA and stated that they were cleared to FL380. They CA 12-12b 01 FEBRUARY 2017 Page 3 of 22

kept the other aircraft visual and followed it on their TCAS and noted that it was continuing descending a few hundred feet. The controller again asked the other traffic what altitude they were maintaining, to which they replied that they were still recovering from the RA. Flight SA8053 continued at FL370 and landed at FAOR at 0957Z. 1.1.3 Figure 1 shows the flight path flown by SA8053 from shortly after take-off from Moshoeshoe International Aerodrome near Maseru in Lesotho. The track is indicated by the red line (which actually consists of red dots). The green track is that of flight BA6234, which took off from Port Elizabeth. Both aircraft were flying in a northeasterly direction towards position IMGEV, which is indicated in Figure 1. Position OKTEK Position IMGEV Track flown by SA8053 Track flown by BA6234 Figure 1: Radar data displaying the track flown by SA8053 (red) and the track flown by BA6234 (green) 1.2 Injuries to persons 1.2.1 Flight BA6234 Injuries Pilot Crew Pass. Other Fatal - - - - Serious - - - - Minor - - - - None 2 4 130 - CA 12-12b 01 FEBRUARY 2017 Page 4 of 22

1.2.2 Flight SA8053 Injuries Pilot Crew Pass. Other Fatal - - - - Serious - - - - Minor - - - - None 2 1 16-1.3 Damage to aircraft 1.3.1 Neither of the two aircraft sustained any damage as a result of the loss in separation. 1.4 Other damage 1.4.1 No other damage was caused. 1.5 Personnel information 1.5.1 Pilot-in-command (PIC) of ZS-ZWS Nationality South African Gender Male Age 45 Licence number 0270241276 Licence type Airline transport Licence valid Yes Type endorsed Yes Ratings Instrument, MNPS/RVSM, RNP-AR-APCH, A-RNP- APCH, RNP-APCH Medical expiry date 30 June 2017 Restrictions None Flying experience: Total hours 12 017 Total past 90-days 202 Total on type past 90 days 202 Total on type 6 762 CA 12-12b 01 FEBRUARY 2017 Page 5 of 22

1.5.2 First Officer (FO) of ZS-ZWS Nationality South African Gender Male Age 34 Licence number 0270482839 Licence type Airline transport Licence valid Yes Type endorsed Yes Ratings Instrument, MNPS/RVSM, RNP-AR-APCH, Instructor, test pilot Medical expiry date 31 May2017 Restrictions None Flying experience: Total hours 9 417.3 Total past 90-days 199.9 Total on type past 90-days 141.1 Total on type 584.5 1.5.3 Pilot-in-command (PIC) of ZS-SNX Nationality South African Gender Male Age 33 Licence number 0272326604 Licence type Airline transport Licence valid Yes Type endorsed Yes Ratings Instrument, MNPS/RVSM, A-RNP-APCH, instructor, test pilot Medical expiry date 28 February 2018 Restrictions None Flying experience: Total hours 4401.5 Total past 90-days 86.9 Total on type past 90-days 86.9 Total on type 1680.5 CA 12-12b 01 FEBRUARY 2017 Page 6 of 22

1.5.4 First Officer (FO) of ZS-SNX Nationality South African Gender Male Age 25 Licence number 0272342221 Licence type Airline Transport Licence valid Yes Type endorsed Yes Ratings Instrument, instructor, test pilot Medical expiry date 31 August 2017 Restrictions None Flying experience: Total hours 2196.3 Total past 90-days 98.3 Total on type past 90-days 98.3 Total on type 59.3 1.5.5 Radar Controller Nationality South African Gender Male Age 49 Licence number 0331 Licence type Air Traffic Services Licence valid Yes Medical expiry date 30 September 2017 1.6 Aircraft information Figure 2: The aircraft ZS-ZWS (photograph obtained from the internet) CA 12-12b 01 FEBRUARY 2017 Page 7 of 22

Airframe: Type Boeing 737-800 Serial number 32732 Manufacturer Boeing Aircraft Company Year of manufacture 2002 Total airframe hours (at time of incident) 48 055 Last phase inspection (hours & date) 48 009 7 March 2017 Hours since last A check 46.00 C of A (issue date) 18 April 2011 C of A (expiry date) 18 April 2018 C of R (issue date) (Present owner) 12 April 2011 Operating categories Standard Part 121 TCAS Version 7.0 Engine No. 1: Type CFM56-7B Hours since new 47500 Engine No. 2: Type CFM56-7B Hours since new 37060 Figure 3: The aircraft ZS-SNX (photograph obtained from the internet) CA 12-12b 01 FEBRUARY 2017 Page 8 of 22

Airframe: Type Embraer 135-LR Serial number 145620 Manufacturer Embraer S.A. Year of manufacture 2003 Total airframe hours (at time of incident) 24 822.55 Last phase inspection (hours & date) 24 525.7 12 January 2017 Hours since last inspection 296.85 C of A (issue date) 18 April 2011 C of A (expiry date) 27 January 2018 C of R (issue date) (Present owner) 22 January 2010 Operating categories Standard Part 121 TCAS Version 7.0 Engine No. 1: Type Hours since new 22910.29 Rolls Royce AE3007 Engine No. 2: Type Hours since new 31182.10 Rolls Royce AE3007 1.7 Meteorological information Wind direction 280 Wind speed 36 kts Visibility 9999 m Temperature ISA+6 Cloud cover Nil Cloud base N/A 1.8 Aids to navigation 1.8.1 Both aircraft were on autopilot following a pre-programmed flight plan. CA 12-12b 01 FEBRUARY 2017 Page 9 of 22

1.9 Communication 1.9.1 All communication was carried out on the Johannesburg Area South East VHF frequency 132,15 MHz 1.10 Aerodrome information 1.10.1 Both aircraft were en route to FAOR under radar control. 1.11 Flight recorders 1.11.1 Both aircraft were equipped with a flight data recorder (FDR) and a cockpit voice recorder (CVR). No information was downloaded from either of these devices for the purpose of this investigation, as both aircraft remained in service following the incident. 1.12 Wreckage and impact information 1.12.1 Not applicable. 1.13 Medical and pathological information 1.13.1 Not applicable. 1.14 Fire 1.14.1 There was no pre- or post-impact fire. 1.15 Survival aspects 1.15.1 This was a survivable incident. There were no injuries to any of the occupants on board either of the aircraft. CA 12-12b 01 FEBRUARY 2017 Page 10 of 22

1.16 Tests and research 1.16.1 Radar data The radar data of the incident were viewed by the investigating team at the facility of the service provider and the controller was also interviewed during this period. It was evident that SA8053 took off from FXMM and climbed to it s allocated flight level of 370 and remained at that altitude until it was cleared for the descent for FAOR. The controller notice the clear level alert monitoring (CLAM) amber warning, which is a system generated warning to alert the controller of a violation, Cleared Flight Level entered into the controllers display. The CLAM warning is also prompted by an audio alert warning. It was noted that flight BA6023 had descended below its assigned flight level of FL380 indicating its level at the time to be FL374. The vertical deviation from its assigned flight level was 560 feet, RVSM procedures do not allow for a vertical deviation of more than 200 ft. BA6234 captured at FL374 instead of FL380 SA8053 maintaining its allocated cruise altitude at FL370 Figure 4: The CLAM warning visible on the controllers radar screen CA 12-12b 01 FEBRUARY 2017 Page 11 of 22

Left turn by BA6234 to ETLIG Position IMGEV Figure 5: Both aircraft flying overhead position IMGEV in a north-easterly direction Figure 6 provides the vertical flight path of the two aircraft after crossing position IMGEV with flight BA6234 already on the descent from FL410 to FL380. Flight SA8053 remained at FL370. Figure 6 also indicates the position where the crew of flight BA6234 commenced with the left turn towards position ETLIG as per the instructions of the controller. CA 12-12b 01 FEBRUARY 2017 Page 12 of 22

Crew of BA6234 commence with the left turn to ETLIG while on the descent. Figure 6: Vertical flight path display of the two aircraft 1.17 Organizational and management information 1.17.1 None was considered necessary for the investigation as both operators were in possession of valid air service licences as well as air operating certificates (AOC). 1.18 Additional information 1.18.1 Definition (EUROCONTROL) A level bust or altitude deviation is defined as any unauthorised vertical deviation of more than 300 feet from an air traffic control (ATC) flight clearance while flying in controlled airspace. Within reduced vertical separation minima (RVSM) airspace this limit is reduced to 200 feet. RVSM airspace is the airspace capacity between FL290 and FL410 inclusive. This operational hazard may result in serious harm either from an actual mid-air collision or from a rapid avoidance manoeuvre. 1.18.2 ICAO Annex 6, Chapter 4, Flight Operations Reference: Sub-Chapter 4.4, In-flight Procedures CA 12-12b 01 FEBRUARY 2017 Page 13 of 22

4.4.10 Aeroplane operating procedures for rates of climb and descent Recommendation.- Unless otherwise specified in an air traffic control instruction, to avoid unnecessary airborne collision avoidance system (ACAS II) resolution advisories in aircraft at or approaching adjacent altitudes or flight levels, operators should specify procedures by which an aeroplane climbing or descending to an assigned altitude or flight level, especially with an autopilot engaged, may do so at a rate less than 8 m/sec or 1 500 feet/min (depending on the instrumentation available) throughout the last 300 m (1 000 feet) of climb or descent to the assigned level when the pilot is made aware of another aircraft at or approaching an adjacent altitude or flight level. The ASR in question is #6984, dated 13 March 2017. The relevant Comair SOP can be found in Part 1, Section 9, Paragraph 26.6 (TCAS Policy and Procedures; Rate of Climb/Descend Restriction) 26.6 Rate of Climb/Descend Restriction The SACAA has given the following dispensation to the Operator: It is recommended that the operator s aircraft be operated as follows: a. Climb and descend rates in RVSM airspace and transition areas shall be limited to 1000ft/min when operating within 5nm and 2000ft of other aircraft to minimise the generation of TA s and RA s. b. Reduce the ROD/ROC to less than 1500ft/min in vertical speed mode when a TA is anticipated or indicated. c. Operate the aircraft according to the Boeing AFM utilising the VNAV, LVL CHG or VS functions by operating the aircraft in the above recommended manner both the manufacturer s operating procedure and the CAR 91.07.32 shall be complied with. Note. - Material concerning the development of these procedures is contained in the PANS-OPS (Doc 8168) Volume I, Part III, Section 3, Chapter 3. CA 12-12b 01 FEBRUARY 2017 Page 14 of 22

1.18.3 The traffic collision and avoidance system (TCAS) was designed to minimise the risk of a mid-air collision by providing early detection and warning to aircraft equipped with the system. 1.18.4 When an aircraft is within 20 nm of the TCAS-equipped aircraft, an intruder alert is generated. Once the intruder is within 3.2 nm or 40 seconds from impact, a traffic advisory (TA) is generated with an aural caution (see figure 7, top) 1.18.5 If the intruder is within 2.5 nm or 25 seconds from impact, a resolution advisory is generated (see figure 7, bottom). If both approaching aircraft are equipped with TCAS, a resolution to separate the aircraft will be generated. If only one aircraft is so equipped, then only that aircraft will be given a pitch change to avoid the intruder. CA 12-12b 01 FEBRUARY 2017 Page 15 of 22

Figure 7: Examples of a traffic advisory (top) and a resolution advisory (bottom) (Source; https://www.slideshare.net/theoryce/autoflight-part-1) CA 12-12b 01 FEBRUARY 2017 Page 16 of 22

Figure 8: TCAS regions (Source: Flight Safety Information) 1.19 Useful or effective investigation techniques 1.19.1 No new methods were applied. 2. ANALYSIS 2.1 Man (cockpit crew) The cockpit crew of BA6234 had preprogramed their FMC to comply with the Standerton 1C Standard approach. Once the controller cancelled the STAR and routed the flight direct to ETLIG, the FMC s current vertical navigation was not optimised to meet the vertical bearing for the waypoint. Once the resolution advisory warning was activated, the PF disconnected the AP and AT and complied with the TCAS level-off command. Once the clear of conflict message had been generated, the aircraft had descended between 400-600 ft below the assigned altitude. The aircraft was then stabilised and returned to FL380. CA 12-12b 01 FEBRUARY 2017 Page 17 of 22

2.2 Machine (aircraft) Figure 9: The mode control panel (MCP) and the indication on the primary flight display. (Source: https://www.slideshare.net/theoryce/autoflight-part-1) 2.2.1 If the ALT HOLD push button (red square above) is selected, the aircraft will vertically navigate to the selected Mode Control Panel (MCP) altitude as shown in the window. 2.2.2 The ALT HLD light will come on and ALT HOLD pitch mode will be displayed on the PFD. 2.2.3 When at the selected altitude, if it corresponds to the altitude window, a change on the MCP altitude illuminates the ALT HOLD switch light and arms the vertical speed (V/S) mode. 2.2.4 Once the MCP altitude is achieved, LVL CHG, V/S and V/NAV climb and descend functions are inhibited until a new MCP altitude is selected. 2.2.5 During a descent, the auto-throttle maintains at idle thrust, and the aircraft will level off either at MCP altitude or the VNAV path, whichever occurs first. CA 12-12b 01 FEBRUARY 2017 Page 18 of 22

3. CONCLUSION 3.1 Findings Cockpit crew BA6234 3.1.1 Both cockpit crew members were appropriately licensed in accordance with the regulatory requirements and held the required ratings to conduct the flight. 3.1.2 Both cockpit crew members held valid aviation medical certificates issued by a SACAA-designated aviation medical examiner (DAME). 3.1.3 The crew received a TCAS RA warning in the cockpit during the descent from FL410 to FL380. Cockpit crew SA8053 3.1.4 Both cockpit crew members were appropriately licensed in accordance with the regulatory requirements and held the required ratings to conduct the flight. 3.1.5 Both cockpit crew members held valid aviation medical certificates issued by a SACAA-designated aviation medical examiner (DAME). 3.1.6 The crew received a TCAS TA warning in the cockpit, with the indication that an aircraft at a higher altitude was descending. The crew were able to visually identify the aircraft on their left. Aircraft 3.1.7 The Boeing 737-800 was equipped with TCAS II version 7.0, which was fully functional during the flight. The crew received an RA warning while on the descent. 3.1.8 The Embraer 135 was equipped with TCAS II version 7.0, which was fully functional during the flight. The crew received a TA warning while maintaining their cruise altitude at FL370. 3.1.9 On both aircraft, the cockpit voice recorders (CVRs) were overwritten as both aircraft remained in service following this incident. CA 12-12b 01 FEBRUARY 2017 Page 19 of 22

3.1.10 Both aircraft were technically capable of meeting the stringent altimetry system performance requirements to ensure RVSM flight minima could be adhered to. 3.1.11 The communication devices (radios) on board both aircraft were serviceable during the duration of their respective flights. 3.1.12 There were no relevant technical issues with either of the two aircraft. Radar Controller 3.1.13 The area controller held a valid air traffic service licence and was appropriately rated to perform his duties. 3.1.14 Both aircraft were adhering to IFR flight rules and were flying in a north-easterly direction overhead position IMGEV. 3.1.15 The controller received an amber clear level alert monitoring (CLAM) warning on the radar screen when BA6234 descended below the assigned flight level of FL380. 3.1.16 The controller communicated with the crew of BA6234, advising them that they were cleared to FL380 as they descended below the cleared level to FL374. Radar data 3.1.17 Both aircraft were under radar control. 3.1.18 The radar data indicates that flight BA6234 descended 560 feet below its assigned level to FL374 before the crew returned the aircraft to FL380. 3.1.19 Flight SA8053 remained at its assigned flight level (FL370) and did not deviate from it at any stage. RVSM minima 3.1.20 In order to meet RVSM minima, an aircraft is not allowed an unauthorised vertical deviation of more than 200 feet from an air traffic control (ATC) flight clearance while flying in controlled airspace. CA 12-12b 01 FEBRUARY 2017 Page 20 of 22

Environment 3.1.21 This incident occurred during daylight conditions, with clear sky conditions prevailing. 3.1.22 Turbulence was not a factor during this incident. 3.1.23 The weather conditions at the time had no influence on the incident. Investigation 3.1.24 This incident was received via an e-mail reporting system used by the air traffic control services in South Africa that forwarded it to the regulating authority the day after the incident occurred. Since both aircraft remained in service following the incident, the CVR recording capacity on both aircraft was exceeded, and the investigators were therefore deprived of information that might have made it possible to identify potential safety deficiencies in terms of flight crew coordination either before or after the TCAS advisory, as well as the appropriateness of the operation of TCAS. 3.2 Probable cause 3.2.1 After flight BA6234 was rerouted direct to ETLIG, the flight management computer required a faster descent rate in order to accomplish the planned vertical bearing for ETLIG. The crew began the descent from FL410 to FL380 but inadvertently (whether due to a human or machine error could not be established) descended through the assigned level before levelling off following a resolution advisory (RA). 4. SAFETY RECOMMENDATIONS None 5. APPENDICES 5.1 Annexure A (FAOR - Standerton 1C, Standard Arrival Chart for runway 03R) CA 12-12b 01 FEBRUARY 2017 Page 21 of 22

ANNEXURE A FAOR - Standerton 1C, Standard Arrival Chart for runway 03R CA 12-12b 01 FEBRUARY 2017 Page 22 of 22