MIPDANIO is the common mnemonic of the standard procedure for sending a Mayday alert via VHF or any similar means of communication. It is essential that Mayday messages, or indeed any emergency radio broadcast, are concise and clear and having standard information in a recognisable order is a perfect way to get your information understood, and help on its way. Mipdanio is a really good way of remembering what essential information to send when in a fluster in an emergency situation.
It stands for:
Mayday
Identification
Position
Distress (eg. Fire, Collision etc)
Assitance Required
No. of people onboard
Information (eg. abandoning to liferaft)
Over
So an example of a Mayday message, with the correct procedure should read something similar to:
Mayday, Mayday, Mayday,
Yacht Trouble, Yacht Trouble, Yacht Trouble
Mayday, Yacht Trouble
Our position is 50.35N, 001.45W, 315 degrees off Garrison Point, 4 miles.*
We are holed and sinking
Immediate Assistance Required
There are 4 people on board
We have no liferaft, and are firing rocket flares every 3 minutes
Over
After a Mayday is sent, you should wait for acknowledgment, either from the coastguard, or from another vessel so that you know help is on its way. If possible, resend your message every few minutes until you get a response (or until your batteries are flooded...)
There are a few additional things to remember.
- Check your VHF unit is ON
- Ensure you are on Channel 16
- Ensure you are on Full Power, not Low Power
- If you have a DSC (Digital Selective Calling) unit, then your MMSI (Mobile Maritime System Identification) number should be included in the ID section, or your call sign if you do not have a DSC unit.
- Speak clearly and slowly to ensure you are understood
Only send a Mayday if there is grave and imminent danger to Life, Vessel, Vehicle or Aircraft. It should not be sent in Any Other Circumstances, but a Pan-Pan call should be made instead.
* Position can be given as a GPS reading, or as a bearing From a known point. (Something that appears on the chart) The standard procedure is BOD, Bearing, Object, Distance. Or both if you have time. | 
