AVIATOR 200: Preventing Service Interruptions
In fleets equipped with the Cobham AVIATOR 200, interruptions typically originate from three sources: RF, power, and IP network. If the LGA is positioned close to VHF/UHF antennas or in the shadow of the empennage, the terminal loses signal during prolonged turns. Ensure the radome is oriented towards the nose and that coaxial cables remain within permitted attenuation limits, with connectors properly crimped and torqued. The SDU requires positional data; without a stable GNSS feed or an ARINC 429 input carrying lat/lon, beam switching becomes erratic and deregistrations occur. If using NMEA, verify the exact baud rate and format of the port and confirm that TX/RX lines are not inverted in the harness. On the power side, 28 VDC with voltage drops during engine start causes silent resets; check earthing and voltage drop along the supply path. Heat build-up in the cabin degrades RF output power; without adequate airflow the SDU throttles back and periodic disconnections will be observed. GEO latency is typically 600–1200 ms RTT; firewalls with aggressive DPI or timeout settings will drop TCP during the handshake. Set MSS to 1350–1380 and effective MTU to approximately 1400 to avoid fragmentation in VPN/TLS tunnels; MSS clamping provides a significant improvement. Disable automatic updates and background synchronisation tasks; SBB becomes saturated by bursts of connections. For SIP voice, use short keep-alives and maintain stable registration; an adaptive jitter buffer prevents echo under load. For IPsec, reduce DPD intervals and enable NAT-T; excessively frequent probes penalise the satellite link. QUIC/HTTP3 can complicate QoS management; for critical traffic, forcing HTTP/2 over TCP is generally more stable. DNS with large EDNS payloads (>1200 B) causes packet loss; limit UDP payload size and enable fallback to TCP. The USIM must be correctly provisioned; an unactivated IMEI/IMN causes attach loops with no clear symptoms. Changing profiles in flight without restarting the SDU leaves zombie sessions; a controlled restart clears the control plane. To isolate RF issues from IP issues, examine SDU counters: if there are no RF errors but TCP retransmission is high, the problem lies in the network. Include a smoke test in the pre-flight procedure: registration, SBB carrier acquisition, extended ping, voice call, and basic web browsing. If all checks pass and interruptions persist, update the SDU firmware and routing tables; stability fixes are released frequently. Record SDU syslogs and router logs in parallel: the interruption "signature" they provide dramatically reduces troubleshooting time.
NASSAT - Network Satellite Systems