🔍 Key Concepts

• GMDSS sea areas (A1, A2, A3, A4) and what shore infrastructure they rely on • The role of NBDP (SITOR) in long-range text communications compared with VHF and MF radiotelephony • How partial or alternate carriage provisions work when a vessel already carries certain other GMDSS equipment (e.g., INMARSAT, HF DSC)

💭 Think About

• Ask yourself in which sea areas voice-only equipment (like VHF or MF radiotelephone) is clearly not sufficient for distress and safety, making teletype/data services more relevant. • Consider where satellite coverage (like Inmarsat in A3) versus HF radio coverage (used especially in polar or very remote regions) affects whether NBDP is still used or may be substituted. • Think about whether SITOR (NBDP) would be needed in coastal VHF-only areas or whether it is more associated with ocean-going or polar operations.

✅ Before You Answer

• Verify the official GMDSS sea area definitions and what equipment is mandatory in each area under SOLAS and 47 CFR/46 CFR, especially for A3 and A4. • Check which equipment types are allowed as alternatives to one another (e.g., HF + NBDP vs satellite systems) in the regulations or GMDSS carriage tables. • Confirm whether short-range coastal sea areas (A1/A2) rely on NBDP at all, or if they depend primarily on VHF/MF DSC and radiotelephony instead.