Offshore IFR operations questions

[TundraT]

As a land lover I have some question about offshore IFR operations.

1. When you depart from land what altimeter do you set once airborne and is your minimums for the approach offshore a BARO or Radar Altimeter?

2. Also if you are offshore and depart IFR to another offshore location is the approach BARO or Radar Altimeter?

Thanks in advance for the education.

[offshore gezza]

In transit to your rig you will be flight levels or altitude, so standard setting procedures apply.

To effect a radar approach you will normally match your BARO to your radar altimeter and fly to a radar height, dependent on the height of the helideck.

All offshore approaches are flown the same manner. But you must remember to reset your baro back to local QNH, if you changed it of course, before you depart the rig.

hope this helps.

[eivissa]

Depending on the region and operator there seem to be different procedures. Below 1000ft Rad-Alt this becomes the essential instrument and limiting number. Bar-Alt is never adjusted to the Rad-Alt, but difference between the two is briefed during the pre-descend check list. If Rad-Alt goes in-op a safety margin is added on top of the bar-alt. 200ft in our case.

[Um... lifting...]

Depends. Where are you operating, geographically?

Some parts of the world use QFE in the airport environment, QNH when clear of controlled airspace and standard passing through the transition level (quite low some places). And that's just the baralt.

Others use QNH throughout and one may never go through the transition level and an offshore platform may or may not offer a particularly accurate QNH in some places.

Some bits of offshore water in this world aren't at sea level or even particularly close to it, in which case offshore gezza's method can get one in a world of trouble. In those cases, it's advisable and usually procedural to use the radalt while leaving the baralt at local QNH, at least once one commences descent. Most offshore IFR approaches are predicated on the radalt. This will all be spelled out in one's SOPs.

In transitioning from one platform to another in the same body of water, one usually uses the same altimeter one was using for the first one for the second one.

So, it depends.

[offshore gezza]

you are both absolutely correct, my apologies.

ARA's are flown on the rad alt, primarily, unless broken of course.

when i say set BARO to rad alt, this is done to avoid confusion when looking at different altimeters. your standby alt is still set to QNH.

in the aircraft i fly the BARO is on the PFD and the rad alt is on the NMD, so its easier to align the two so that the PFD becomes your primary instrument.

[TundraT]

Thank you one and all for the insight.