Safety Investigation Report 2018:1 Factual Information/1.9/1.9.4 ACARS
SAFETY INVESTIGATION REPORT MH370 (9M-MRO)
Sub-page List
- 1 Factual Information/1.9/1.9.4 ACARS/1
- 1 Factual Information/1.9/1.9.4 ACARS/1/APU Report
- 1 Factual Information/1.9/1.9.4 ACARS/1/Link Established
- 1 Factual Information/1.9/1.9.4 ACARS/1/Loadsheet
- 1 Factual Information/1.9/1.9.4 ACARS/1/NOTOC
- 1 Factual Information/1.9/1.9.4 ACARS/1/Position Report
- 1 Factual Information/1.9/1.9.4 ACARS/1/Printer
- 1 Factual Information/1.9/1.9.4 ACARS/1/Take-off and Climb
- 1 Factual Information/1.9/1.9.4 ACARS/Intro
1.9.4 Aircraft Communications Addressing and Reporting System
The Aircraft Communications Addressing and Reporting System (ACARS) is a digital data-link system that manages flight plan and maintenance data between the aircraft and the Ground Service Provider (GSP) by using radio i.e. VHF or satellite communications (SATCOM) as shown in Figure 1.9B (below).
Figure 1.9B - ACARS System
Source:
Safety Investigation Report MH370/01/2018
ACARS provides message communication between aircraft and its base (ground). The following messages are transmitted:
- Out of the gate, Off the ground, On the ground, and Into the gate (OOOI) events:
- Out of the gate event: Departure from the gate with all doors closed and parking brake released;
- Off the ground event: Take-off with the nose gear squat switch extended;
- On the ground event: Touch down with the nose gear squat switch compressed; and
- Into the gate event: Parked at the gate with the parking brake set and the door open.
- Flight plans: ACARS interfaces with Flight Management Systems (FMS) acting as the communication system for flight plans to be sent from the ground to the FMS. This enables the aircraft to update the FMS while in flight and allows the flight crew to evaluate the alternative flight plans including the status of connecting flights.
- Weather information: ACARS interfaces with FMS, acting as the communication system for weather information to be sent from the ground to the FMS. This enables the aircraft to update the FMS while in flight and allows the flight crew to evaluate new weather conditions.
- Equipment health: ACARS is used to send information from the aircraft to ground stations about the conditions of various aircraft systems and sensors in real-time. Maintenance faults and abnormal events are also transmitted to ground stations along with detailed messages, which are used by MAS for monitoring equipment health, and to better plan the repair and maintenance activities.
- Aircraft positions which provide latitude and longitude, altitude, speed, total air temperature, total remaining fuel, wind direction and speed and heading.
- Engine performance data which provide engine data during take-off, climb, cruise and approach.
ACARS interfaces with the Multifunction Display (MFD) in the cockpit, which flight crew can use to send and receive technical messages and reports to or from ground stations, such as a request for weather information or clearances or the status of connecting flights. The response from the ground station is received on the aircraft via ACARS as well. The ACARS Manager page in the Communications main menu on the selected Multifunction Display (MFD) is used for this purpose. The COMM display switch, located on the display select panel, displays the communications main menu on the selected MFD. The ACARS Manager page allows the flight crew to independently select/deselect VHF or SATCOM transmission of data.
The ACARS communicates through either the VHF or the SATCOM systems. The ACARS datalink connects to the Satellite Data Unit (SDU) of the SATCOM system and the Center and Right VHF Communication Transceivers of the VHF systems. The Center VHF exchanges data with the ACARS modem in the Communications Core Processor Module (CPM/Comm) of the Left AIMS cabinet. The right VHF exchanges data with the ACARS modem in the CPM/Comm of the Right AIMS cabinet. The ACARS does not interface with the Left VHF Transceiver.
For the ACARS operation the Data Communication Management Function (DCMF) of the AIMS uses the voice/data select to set the VHF Communication Transceiver to the data signal mode. At power-up, the DCMF sets the Center VHF Communication Transceiver to the data signal mode. If the Center VHF Communication Transceiver fails, or voice is selected manually by the flight crew, the DCMF selects SATCOM for data transmissions. If SATCOM fails, the DCMF selects the Right VHF Communication Transceiver for data transmissions. The Left VHF Communication Transceiver is voice only. On the event flight, as instructed by Ground Operations via text message shown on the MFD (shown as ‘Switch VHF3 to Voice’), the flight crew would have selected voice on the Center VHF resulting in SATCOM being used for the data transmissions. Refer to page 1 of Appendix 1.9A – ACARS Traffic Log. The use of SATCOM for the ACARS transmissions is evident in the SATCOM Ground Station Logs [refer to Section 1.9.5, para. 4)]. This switching from VHF to SATCOM for the data transmissions is normal practice in MAS for commercial reasons.
In the event that the aircraft ACARS unit has been silent for longer than a pre-set time interval, the ground station can ping the aircraft (directly or via satellite). A ping response indicates a healthy ACARS communication. This ping is different from the Satellite ping or handshake.
Pre-set time interval for MAS B777 is 30 minutes. When the aircraft ACARS is silent for more than 30 minutes, MAS Operation Control Centre (OCC) is required to send a text message via ACARS to the cockpit or to call the cockpit via SATCOM.
1) Aircraft Communications Addressing & Reporting System Traffic Log
ACARS traffic log messages sent/received to/from 9M-MRO between 1554:41 UTC, 07 March 2014 [2354:41 MYT, 07 March 2014] until 1815:25 UTC, 07 March 2014 [0215:25 MYT, 08 March 2014] is shown in Appendix 1.9A. Some key events are extracted and explained below.
At 1554:41 UTC, 07 March 2014, ACARS data link was fully established on SATCOM transmission and at 1556:08 UTC the flight information (FI) MH0370 and Aircraft Number (AN) 9M-MRO were keyed in by the crew as per Figure 1.9C (below).
Figure 1.9C - ACARS data link established SATCOM transmission
Source:
Safety Investigation Report MH370/01/2018
Notice to Crew (NOTOC) was sent at 1606:15 UTC on 07 March 2014 [0006:15 MYT, 08 March 2014] direct to the aircraft printer and to be printed out by the crew.
NOTOC from the ground station to the cockpit stated the special loads of total 4,566 kg of mangosteens were carried on board. Details of the mangosteens were:
- 1,128 kg at station 41L,
- 1,152 kg at station 41R,
- 1,148 kg at station 43L, and
- 1,138 kg at 44L respectively.
(Refer to Section 1.18.2 for details of cargo carried).
Declaration of “there is no evidence that any damaged or leaking packages containing dangerous goods have been loaded on the aircraft at this station” was also written in the NOTOC message. Figure 1.9D (below) shows the snapshot of the ACARS NOTOC message.
Figure 1.9D - Snapshot of ACARS NOTOC message
Source:
Safety Investigation Report MH370/01/2018
Aircraft final loadsheet was sent via ACARS at 1606:32 UTC, 07 March 2014 [0006:32 MYT, 08 March 2014] direct to the aircraft printer and to be printed out by the crew. Details of aircraft weight as stated in the final loadsheet are discussed in Section 1.6.5.
Figure 1.9E (below) shows the snapshot of the final loadsheet of this aircraft.
Figure 1.9E - Final Loadsheet
Source:
Safety Investigation Report MH370/01/2018
Pilot acknowledgement and confirmation of the final loadsheet is shown in the ACARS snapshot in Figure 1.9F (below).
Figure 1.9F - Final Loadsheet Acknowledgement
Source:
Safety Investigation Report MH370/01/2018
Data on aircraft APU is shown in Figure 1.9G (below). APU report generated by ACMS sent via ACARS at 1629:33 UTC stated the total APU cycles and hours were 15,699 cycles and 22,093 hours. APU hours for the previous flight was 4 hours.
Figure 1.9G - APU Report
Source:
Safety Investigation Report MH370/01/2018
Engine take-off and climb reports transmitted via ACARS are explained in Section 1.6.4 para. 8). Engine parameter reports were transmitted to MAS and then to Rolls Royce for Engine Health Monitoring (EHM). Appendix 1.9A shows these data in coded form. The decoded data are shown in Appendix 1.6B.
The first (which was also the last) position report was transmitted via ACARS at 1707:29 UTC, 07 March 2014 [0107:29 MYT, 08 March 2014]. This was a collation of 6 reports generated at 5-minute intervals by the system at 1641:43 UTC, 1646:43 UTC, 1651:43 UTC, 1656:43 UTC, 1701:43 UTC and 1706:43 UTC, 07 March 2014. Parameters transmitted are as per Table 1.9A (below). The actual traffic log on the position report is reproduced in Figure 1.9H (below). Position reports were programmed to be transmitted every 30 minutes.
Note: Aircraft position information is also included in the EHM take-off and climb reports.
| Greenwich Mean Time (GMT) - UTC | 1641:43 | 1646:43 | 1651:43 | 1656:43 | 1701:43 | 1706:43 |
| Altitude (ALT) – Feet | 103 | 10,582 | 21,193 | 28,938 | 34,998 | 35,004 |
| Calibrated Airspeed (CAS) - Knots | 168.4 | 261.8 | 301.1 | 303.1 | 278.0 | 278.4 |
| MACH | 0.255 | 0.478 | 0.669 | 0.783 | 0.819 | 0.821 |
| Total Air Temperature (TAT) - °C | 31.1 | 23.4 | 11.6 | 2.6 | -13.4 | -13.1 |
| Static Air Temperature (SAT) - °C | 27.3 | 10.4 | -11.8 | -27.4 | -43.9 | -43.8 |
| Latitude (LAT) | 2.767 | 3.074 | 3.553 | 4.109 | 4.708 | 5.299 |
| Longitude (LONG) | 101.715 | 101.760 | 101.988 | 102.251 | 102.534 | 102.813 |
| Gross Weight (GWT) – lb | 492,520 | 489,200 | 486,240 | 483,840 | 481,880 | 480,600 |
| Total Remaining Fuel Weight (TOTFW) - kg | 49,200 | 47,800 | 46,500 | 45,400 | 44,500 | 43,800 |
| Wind Direction (WINDIR) | 140.3 | 107.6 | 91.8 | 58.4 | 69.6 | 70.0 |
| Wind Speed (WINDSP) | 1.25 | 9.38 | 19.50 | 10.63 | 17.38 | 17.13 |
| True Heading (THDG) | -33.5 | 27.3 | 27.8 | 26.0 | 26.8 | 26.7 |
| Note: Values in bold have been corrected using data from the original ACARS position report. | ||||||
Table 1.9A - ACARS Position Report
Source:
Safety Investigation Report MH370/01/2018
1.9 Communications
Figure 1.9H - Position Report
Source:
Safety Investigation Report MH370/01/2018
The first message sent to the aircraft cockpit printer from the MAS ODC was at 1803:23 UTC. The ACARS message requested the crew to contact the HCM ACC immediately. The incoming downlink message at 1803:24 UTC showed the message failed to reach the aircraft. Messages are auto transmitted every 2 minutes and the message was retransmitted until 1843:33 UTC but all messages failed to get a response. Automated downlink message by ACARS showed ‘failed’. Message sent to the aircraft cockpit printer and the Automated Downlink messages are shown in Figures 1.9I and 1.9J (below), respectively.
Figure 1.9I - Message from MH ODC
Source:
Safety Investigation Report MH370/01/2018
Figure 1.9J - Automated Downlink Message
Source:
Safety Investigation Report MH370/01/2018