BARO/Radio minima Setting

[Jack1985]

Hi I understand pilots use this feature for MDH, Incases of ILS CAT II radio minima is used so say in a 737ng landing in Cork on RWY17 the pilot would set the radio minima to 60 (The RDH being 57) if below CAT II he will use baro minima which usually is around 200ft AGL so let's say at Cork that would be 700ft for baro minima. I find this easy to understand however I noticed during a turnaround today a BARO setting which I can't remember was displayed on the PFD, the plane was departing and the setting was in the thousands, my question is what is baro setting on departure used for and what is it set to, also would it vary like approach minima's?

Would appreciate a response, thank you! :)

[Pylut737]

If I understand your question correctly, in Ireland the Altimeter should read field elevation upon landing and again upon departure. If you glanced into the cockpit and saw an altitude in the thousands, I suspect it the aircraft was sitting on the ground for quite some time and the local pressure has decereased yeilding a higher indicated altitude.

[westhawk]

The only thing which should be indicating in the thousands on departure from anywhere in Ireland should be the altitude pre-select! The altitude initially cleared to by ATC will normally be set prior to departure.

Changes in local altimeter setting only account for much smaller increments of approximately 10' per hundredth of an inch hg or about 30' per hectopascal change in altimeter setting. I've seen it change by as much as 400' overnight but even that was a pretty significant weather front passage. Large tropical cyclones can produce much more dramatic pressure gradients.

Radar altitude will read somewhere near zero while the aircraft is on it's wheels unless malfunctioning.

[Denti]

Some airlines set their single engine acceleration altitude as baro minimum on the ground for departure. That way there will be a visible reminder on the altitude tape in case of an engine failure even if the FMC fails as well.

[renard]

On the aircraft I fly, the minimums is normally set to BARO.

It's default setting is 2000. Perhaps you saw something like that.

[Jwscud]

In my mob, if you are doing a CAT I or NPA, minima are set on the baro to the foot. If CAT II/III, the minima are set on the radio to the foot. The MFRA is set in the baro.


Before departure, we set the MFRA on the baro, which is normally 1000' AFE. I imagine that was what you saw.

[Jack1985]

Hi guys thanks for your answers! :)

I can see how some the question kind of confused a few of you, the local setting was already inputted as 1002 Hpa which was correct but displayed above that to the left - but still in the right side of the screen the figure BARO 1,500 was displayed as pointed out (The figures renard & Jwscud) jogged my memory.

Some airlines set their single engine acceleration altitude as baro minimum on the ground for departure. That way there will be a visible reminder on the altitude tape in case of an engine failure even if the FMC fails as well.

So after seeing 1,500ft displayed as BARO is this the thrust reduction altitude? Which I know varies on thrust setting (CLB, CLB1 or CLB2).

[737aviator]

1502ft would be the MFRA set before departure on the Baro mins for Cork so that was definitely what you saw.

If NADP2 then that would be the standard acceleration height or in case of engine failure it would also be.
Thrust reduction occurs at 1500ft AGL irrespective of the NADP procedure in use presuming your 737NG belonged to who I think it did. ;)

Another possibility for a high baro setting would be a NPA, Circling Approach or visual approach (land altitude plus 500ft is set).

[Jack1985]

Thank you 737aviator :)

[TyroPicard]

OK I give up.... wot's MFRA stand for?

[eckhard]

Minimum Flap Retraction Altitude