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By Hazel C
#1255759
Just a quick one. So, when calculating a safety height, its 1000ft + 500ft for terrain and 300ft for obstacle clearance? so MSA is 1800ft above given MSA on chart?

Or do I need to round up the given figures for obstacles and terrain too/instead?

Military Rules state "add 1000ft onto the alt of highest fixed obstacle then round up to the next 100ft" Is this the same in civvy street. I ask as Pooleys give me the impression that one always adds 1000ft for safety, and since the charts don't show terrain under 500ft, then one adds 500 ft and as the charts dont show obstacles under 300ft, then add 300ft, so basic MSA is 1800ft. Then of course you have the MSA given on the chart to add to that.

I'm confused, could someone help explain this please? Thanks :?
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By Genghis the Engineer
FLYER Club Member  FLYER Club Member
#1255761
MSA is an IFR concept, and doesn't apply to a VFR pilot. But for the record, it's 1000ft above any obstacle within 5nm of track, normally rounded up to the nearest 100ft for convenience - made relatively simpler by conservatively using the numbers marked on the chart for half degree grid rectangles. That's what you're describing as "military rules", which isn't strictly accurate, unless some military training organisations have adopted that locally.

Legally, as a VFR pilot, rule 5 is all that applies to you: 500ft from / 1000ft above built up areas / able to glide clear of same..


In practice, applying the IFR MSA concept to VFR flying, and even adding some extra fat to that as you've done above, is a perfectly sensible way of staying safe, and made very easy by the numbers on the chart and if you do that for PPL training / skill test / everyday flying nobody will ever criticise you for it. But, if questioned by an examiner, be clear that you're simply doing that as a way to be safe and sensible, and recognise that rule 5 is what actually applies.

G
User avatar
By Hazel C
#1255763
Hmm, thanks Genghis.
So I guess then, that Pooleys is written for IFR as well, hence adding the 500ft and 300ft. And I also assume then, that Airquiz is wrong in their answer of rounding up the obstacle AND terrain heights to the next 100ft THEN add 300ft for terrain heights?
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By Genghis the Engineer
FLYER Club Member  FLYER Club Member
#1255767
Basically, yes.

It may be some standard teaching somewhere, and perfectly safe as a planning tool - but it's most definitely not the law anywhere I've flown.

I don't have a Pooleys to hand, but it's not possible you're looking at an example using representative values rather than universal values?

G
By Balliol
#1255780
Contours up to 500 aren't shown, so in theory you could have a 499 contour + 300 obstacle = 799, however when calculating safety altitudes on a typical 500,000 chart at PPL level this will be using the MEFs. These are the top of the highest feature in that quadrant, you add the 1000ft to that for clearance margin and 300ft for possibility of unmarked obstruction. No need for 500 addition as well.

As Genghis says, it's not an MSA so you can operate below safety altitude if visual with the ground, however if in poor vis or unsure of position you should climb to safety altitude while remaining VMC.
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By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1255792
Doesn't the MEF take into account the 300ft objects that aren't marked?
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By Keef
#1255797
I thought it did, but charts vary!

If you're VFR and looking where you are going, as they've said: look out.

IFR is a different set of rules and guidelines. I would be leery of using IFR numbers on a VFR test. Adding lots of safety factors won't hurt you, until you find it puts you into the clouds and you can't see where you are going.
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By Timothy
#1255805
Also, be careful of the expression MSA. It means two different things.

The only ICAO meaning is Minimum Sector Altitude, which is marked on IFR approach plates as being the minimum altitude to descend within certain angles (usually, but not always, quadrants) from a known point (usually, but not always, the ARP or a nav aid on an airfield.) It gives 1000' clearance from surveyed and charted terrain and obstacles, so, as I understand it, no need for the extra 300'.

It looks something like this Image and, I say again, that is the only ICAO usage of MSA.

The MSA as reported on Jepp data in GPSs, is Minimum Safe Altitude, and gives you 1000' (2000' in mountainous areas) above any obstacle within a grid and, if the highest point is terrain rather than obstacle adds 300' for the unknown obstacle. This is not an ICAO usage.

Both of these MSAs are IFR concepts, but they do cause confusion by having the same TLA and referring to rather different, but rather similar, constructs.
User avatar
By Yankee-K
#1255809
From my recent (pre September 2013 or whenever the exams changed) PPL training.

MSA is minimum safety altitude and is required to be calculated and noted on your plog.

It is the height of ground, rounded up to the next 100ft + 300ft for unmarked objects + 1,000ft safety.

As has been pointed out ground on the half-mill chart is not shaded below 500ft so the MSA for that area would be 499ft + 300ft + 1,000ft giving a MSA of 1800ft.

when plotting a route the MSA is calculated for 5nm either side of route PLUS 5nm at each end of each leg.

If you can see where you are going then normal ANO VFR rules apply, 500ft, 1,000ft above built-up areas etc, and glide clear. MSA is a SAFETY altitude.
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By Hazel C
#1255846
Thank you everyone for your replies. No wonder I am confused, as there seems varying views on what the answer is.

Thanks Yankee,

It is the height of ground, rounded up to the next 100ft + 300ft for unmarked objects + 1,000ft safety.

As has been pointed out ground on the half-mill chart is not shaded below 500ft so the MSA for that area would be 499ft + 300ft + 1,000ft giving a MSA of 1800ft.


That seems to fit in most with what Pooleys says, and has answered my question over the 500ft part as well. So I don't think i'll go too far wrong if I use that method.
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By Iceman
FLYER Club Member  FLYER Club Member
#1255857
That would seem to be overly cautious as an MSA which is a figure that, when flying VFR, you'd only be interested in if the weather starts forcing you down. The minimum MSA for VFR when not over built up areas is 500 ft unmarked ground, 300 ft unmarked obstacle, 500 ft Rule 5 equals 1300 ft. Adding another 500 ft to the MSA would be denying you 500 ft of entirely usable airspace precisely when you need it most, I.e., when the weather's closing in around you, and may force you into IMC unnecessarily. I'd therefore advise that arbitrary additional safety height not be added to the MSA as this is likely to cause a greater safety problem than using an accurate MSA figure.

Iceman 8)
User avatar
By Timothy
#1255879
Which is precisely the logic I use for railing against adding stuff to DAs on IAPs. If you don't go down to minima you can actually give yourself all sorts of problems and dangers (go around, missed approach, hold, alternate planning, alternate briefing etc.) all of which might be avoided if you go to minima.

The argument that if you are not in practice you shouldn't go to minima actually applies to all the above (go around, missed approach, hold, alternate planning, alternate briefing etc.) and the argument that IMCR holders are not equipped to go to minima also applies to all the other aspects.

IMHO all IFR pilots, including IMCR holders, should acquire and maintain their ability to go to minima. But no-one listens to me.

[sorry, rant off]
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By QSD
#1255946
I agree with Iceman that adding 1000 ft (or even worse, 1300 ft) to the MELs for VFR flight is just wasting valuable airspace. If you did this in my part of the world (around Tonbridge for example) you would need to fly at 2400 ft underneath the London TMA that starts at 2500 ft. If everyone did that it would soon get a bit crowded, and you would not be able to fly on many days when the cloud base is lower than 2,400.

I teach my students to plan their flights to be no lower than MEL plus 500 ft. Even then, some parts of the flight will need to be flown below the "safety altitude" - the transit underneath the 1500ft Gatwick shelf into Redhill for example. All the more reason to look out of the window!

There is no need to add the 300 ft "unmarked obstacle" allowance to MELs as it already takes that into account.

Using the MELs is a quick way of planning. A slightly better way is to look for the highest ground within 5nm either side of planned track and add 800 ft (i.e. 500 ft plus the 300 ft unmarked obstacle allowance). This will often give a bit more airspace to play with, but takes longer.
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By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1255982
The two VRPs to the north of Cardiff are two ruddy great television/radio masts, Wenvoe and St Hilary. You actually fly past them on the way in/out, with inbounds recommended to be at circuit height (800ft) to avoid outbounds climbing above them. It's good to be able to see them as you fly past! :shock:

At the bottom of the Florida Keys, there are a couple of sectors over the sea which have a Maximum Elevation Figure of 14,200ft! (14.2 in the sectors on the map) This is due to a radar which is a large cable held up by a balloon. There is a restricted area, R-2916 around it so you can see where it is. I've actually flown past and seen the large cable. :shock: As long as you avoid the restricted area, you don't need to stay 1000ft or 500ft or whatever above 14,200ft...

http://skyvector.com/?ll=24.75048963443145,-81.44348144885983&chart=301&zoom=3