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MSA  
User currently offlineXXXX10 From United Kingdom, joined Jan 2000, 777 posts, RR: 0
Posted (12 years 2 days 14 hours ago) and read 4953 times:

Can anyone tell me how minimum Safety Altitude is decided.

It doesn,t seem to relate to the height of the terian?

Many thanks

10 replies: All unread, jump to last
 
User currently offlineJETPILOT From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 1, posted (12 years 2 days 12 hours ago) and read 4918 times:

I havent used a VFR sectional for about a decade but I seem to remeber it being 1000? feet above the highest obstacle in the sector.

JET


User currently offlineDg_pilot From United States of America, joined Sep 1999, 856 posts, RR: 2
Reply 2, posted (12 years 2 days 8 hours ago) and read 4901 times:

Isn't there a MSA on approach plates as well?

User currently offlineNormalSpeed From , joined Dec 1969, posts, RR:
Reply 3, posted (12 years 2 days 7 hours ago) and read 4890 times:


MSA, or Minimum Safe Altitude, provides 1000 feet of obstacle clearance, within 25 NM of the navigational station indicated on the approach plate. For example, right now, I'm looking at the ILS Rwy 24 Approach to Martha's Vinyard, Massachusetts. The MSA part says "MSA MVY 25 NM" Meaning that the MSA is determined in terms of distance from the MVY VOR. And there are different sectors with different altitudes defined by radials from the VOR.

MSA does not provide for navigation or communcation signal reception, only obstacle clearance. It is only for use in emergencies or VFR flight. And, the MSA shown on the approach plate is only valid for that approach. Other MSAs apply to other approaches. And, not every approach has an MSA.

'Speed


User currently offlineThirtyEcho From United States of America, joined Dec 2001, 1639 posts, RR: 1
Reply 4, posted (12 years 2 days 3 hours ago) and read 4877 times:

Actually, it is "Minimum Sector Altitude" unless something changed recently. When all else fails, including the missed approach procedure, go to the MSA.

User currently offlineThirtyEcho From United States of America, joined Dec 2001, 1639 posts, RR: 1
Reply 5, posted (12 years 2 days 3 hours ago) and read 4878 times:

Wait...Of course it is "Minimum Safe Altitude." The altitudes depicted on sectionals are "Minimum Sector Altitude." Sorry.

User currently offlineNormalSpeed From , joined Dec 1969, posts, RR:
Reply 6, posted (12 years 2 days 3 hours ago) and read 4876 times:

Actually, it is "Minimum Sector Altitude" unless something changed recently.

I did a little digging, and this is what I came up with:

In the Abreviations section of my Jepp Airway Manual, MSA is "Minimum Safe Altitude." The same goes for the Pilot/Controller Glossary in the AIM. But, in the AIM section 5-4-5, MSA is written, "Minimum Safe/Sector Altitude." And, the term "MSA" isn't mentioned in FAR part 1. So I suppose that either "safe" or "sector" is acceptable. But if it's alright with you, I think I'm going to keep on saying "safe."

Here's the VFR meaning of MSA:

Anywhere: An altitude allowing an emergency landing without undue hazard to people or objects on the ground.

Over Congested Areas: At least 1000 feet above any object with in a 2000 ft radius of the aircraft.

Over Non-Congested Areas: No closer than 500 feet to any object or person on the surface.

Hope this helps,

'Speed



User currently offlineJETPILOT From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 7, posted (12 years 1 day 20 hours ago) and read 4869 times:

Unless I'm mistaken and I'm sure someone will point it out.....

I've been briefing approach plates for about 8 years now..... I thought MSA on an approach plate was minimum safe altitude, at least thats what I've been calling it.

I thought minimum sector altitude was the large numbers on each sector on a sectional chart indicating the altitude which will give you 1000 feet obstacle clearance in that sector.

?????

JET


User currently offlineNormalSpeed From , joined Dec 1969, posts, RR:
Reply 8, posted (12 years 1 day 13 hours ago) and read 4862 times:

I thought minimum sector altitude was the large numbers on each sector on a sectional chart indicating the altitude which will give you 1000 feet obstacle clearance in that sector.

On a Sectional Chart, that figure is called an "MEF" or Maximum Elevation Figure. This represents the highest known terrain or obstruction (the NOS calls these "features") in the quadrangle, and does not provide obstacle clearance.

IFR Low Altitude enroute charts also have similar figures. Jepp calls it a "MORA" (Minimum Of Route Altitude) and, the NOS calls it an "OROCA" (Off Route Obstacle Clearance Altitude). The OROCA and MORA provide 1000 feet of obstacle clearance in non-mountainous terrain (below 7000' MSL), and 2000 feet of obstacle clearance in mountainous terrain (above 7000' MSL). Also, Jepp prints the MORA figures that are above 14000' MSL in red, suggesting the use of oxygen, and the figures below 14000' MSL in green.

And, IFR High Altitude enroute charts have no such figures - they aren't needed, since their MEAs, unless stated at a higher altitude, are FL180.

'Speed


User currently offlineJETPILOT From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 9, posted (12 years 1 day 6 hours ago) and read 4849 times:

Thanks for clearing that up...... I remeber MEF now.....

Thanks

JET


User currently offlineNormalSpeed From , joined Dec 1969, posts, RR:
Reply 10, posted (12 years 1 day 5 hours ago) and read 4836 times:

On a Sectional Chart, that figure is called an "MEF" or Maximum Elevation Figure. This represents the highest known terrain or obstruction (the NOS calls these "features") in the quadrangle, and does not provide obstacle clearance.

Turns out that what I wrote here isn't quite accurate. MEFs do provide a small amount of obstacle clearance. MEFs are rounded up to the nearest 100 feet, and then adjusted upward 100 to 300 feet, depending on the type of obstacle.

'Speed



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