Minimum safe altitude??
Thread Starter
Join Date: Jul 2010
Location: all alone
Age: 36
Posts: 13
Likes: 0
Received 0 Likes
on
0 Posts
Minimum safe altitude??
if we are coming for an approach for a runway which has an elevation of 100feet,and the MSA on the approach plate shows 9500feet,surely we are to descend and land,,my question is ,,arent we crossin the 9500 limit???since msa assures acceptable obstacle clearance of 1000non and 2000mountaineous,,??
Join Date: Apr 2002
Location: UK
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
if we are coming for an approach for a runway which has an elevation of 100feet,and the MSA on the approach plate shows 9500feet,surely we are to descend and land,,my question is ,,arent we crossin the 9500 limit???since msa assures acceptable obstacle clearance of 1000non and 2000mountaineous,,??
In order to descend below it in IMC (not visual) you should be either under positive radar control or on a published instrument arrival. If you are in any doubt then climb back above MSA.
If you are VMC and visual with terrain then you may descend below MSA keeping clear of all obstacles. By night the rules change slightly and include a requirement to check position by radio or radar aids and an identifiable lit area ( normally the runway ).
Others will have different rules and regs.
Join Date: Sep 2000
Location: Bielefeld, Germany
Posts: 955
Likes: 0
Received 0 Likes
on
0 Posts
pilotsaab,
MSA stands for Minimum *Sector* Altitude, and is the minimum altitude in the sector (a portion of a circle defined by radials from the runway location and a largish radius, shaped like a pie slice; the radials are displayed on the plate) which keeps you appropriately above any terrain within that "slice of the pie". When you are landing, then you are following specific routes (lines whose locations are defined by navaids) which have been specifically surveyed for obstacle clearance.
The airport in a long valley is a typical example. Innsbrück and Cali come to mind. Lowish runway compared with what is in the area, lots of clear space straight in on each end, but high mountains to either side. So, high MSA. An American Airlines flight fell foul of "busting sector altitude" in 1995 on approach to Cali by following what they thought was an ATC clearance (they had misunderstood, and were not corrected on readback). There were of course other factors involved as well.
I take it you are not instrument-rated. It is worth getting copies of training material (textbooks, training publications by the relevant regulator) as reference. However, it won't give you any idea of *how* approaches are designed. For that, you have to go to the relevant technical documentation, which is increasingly to be found on the WWW. Try Googling "TERPS". It will give you US FAA TERPS pages, and especially Wally's TERPS page, which is a mine of useful information.
PBL
MSA stands for Minimum *Sector* Altitude, and is the minimum altitude in the sector (a portion of a circle defined by radials from the runway location and a largish radius, shaped like a pie slice; the radials are displayed on the plate) which keeps you appropriately above any terrain within that "slice of the pie". When you are landing, then you are following specific routes (lines whose locations are defined by navaids) which have been specifically surveyed for obstacle clearance.
The airport in a long valley is a typical example. Innsbrück and Cali come to mind. Lowish runway compared with what is in the area, lots of clear space straight in on each end, but high mountains to either side. So, high MSA. An American Airlines flight fell foul of "busting sector altitude" in 1995 on approach to Cali by following what they thought was an ATC clearance (they had misunderstood, and were not corrected on readback). There were of course other factors involved as well.
I take it you are not instrument-rated. It is worth getting copies of training material (textbooks, training publications by the relevant regulator) as reference. However, it won't give you any idea of *how* approaches are designed. For that, you have to go to the relevant technical documentation, which is increasingly to be found on the WWW. Try Googling "TERPS". It will give you US FAA TERPS pages, and especially Wally's TERPS page, which is a mine of useful information.
PBL
Thread Starter
Join Date: Jul 2010
Location: all alone
Age: 36
Posts: 13
Likes: 0
Received 0 Likes
on
0 Posts
thanks alot PBL and paddy ,,well i am instrument rated but since the airblue incident there have been many questions which were laid down by the non aviation related ppl,i was watchn on television and this ex general manager radar controller was mentioning that he bursted the msa which led to the unfortunate incident but the dude was already executing a circle to land i guess,,so he was already within the area and probably familiar with the locality,,i dont want to speculate though,,but all this speculation before black box retrieval just for the sake of gettin high tv ratings is pathetic,,just needed some brushing up to do on this topic for myself,,,,
Join Date: Sep 2000
Location: Bielefeld, Germany
Posts: 955
Likes: 0
Received 0 Likes
on
0 Posts
Well, comments about the Islamabad accident should probably go there, but there are a couple of pertinent observations.
First, he *obviously* busted MSA. But that is simply a tautological consequence of having hit terrain which MSA keeps you above. It is rather like looking at a car which has left the road on a corner, saying "the driver failed to drive in a manner which assured he safely rounded the corner", observing which laws that contravened, and saying one has explained the accident. All one has done, at most, is classify it.
Second, expect everyone, newspapers and televisual media, even the best ones, to publish mixtures of accurate mixed with inaccurate factual information, pure rubbish masquerading as fact (usually quoted from a third party, to protect the journalist), and, above all, extremely inaccurate speculation as to causes, for at least a week after a major accident. The best quick stuff I have seen in a decade and a half is actually the location-fixing work using photos and Google Earth that people such as Machaca and PJ2 put on the threads after accidents. It is more accurate, quicker, than most news organisations seem to manage. I have myself tried, after accidents, to accumulate accurate information rapidly and not succeeded in getting much information on which I knew I could rely inside about a week and a half. A decade or so later, with all the new technology, that brick wall still seems to be there, but with small holes in it poked by the Google Earth/picture sharing mentioned above.
PBL
First, he *obviously* busted MSA. But that is simply a tautological consequence of having hit terrain which MSA keeps you above. It is rather like looking at a car which has left the road on a corner, saying "the driver failed to drive in a manner which assured he safely rounded the corner", observing which laws that contravened, and saying one has explained the accident. All one has done, at most, is classify it.
Second, expect everyone, newspapers and televisual media, even the best ones, to publish mixtures of accurate mixed with inaccurate factual information, pure rubbish masquerading as fact (usually quoted from a third party, to protect the journalist), and, above all, extremely inaccurate speculation as to causes, for at least a week after a major accident. The best quick stuff I have seen in a decade and a half is actually the location-fixing work using photos and Google Earth that people such as Machaca and PJ2 put on the threads after accidents. It is more accurate, quicker, than most news organisations seem to manage. I have myself tried, after accidents, to accumulate accurate information rapidly and not succeeded in getting much information on which I knew I could rely inside about a week and a half. A decade or so later, with all the new technology, that brick wall still seems to be there, but with small holes in it poked by the Google Earth/picture sharing mentioned above.
PBL
Guest
Join Date: Apr 2009
Location: On the Beach
Posts: 3,336
Likes: 0
Received 0 Likes
on
0 Posts
pilotsaab:
MSAs are not operational altitudes in all countries. Unless you know a particular country's rules very well, MSAs should be relegated to "safety orientation" information.
They are not operational altitudes in the U.S., and they provide only 1,000 feet of vertical clearance, even in designated mountainous areas. Further, in U.S. RNAV IAPs they are not sectorized, which makes them of marginal value (at best) in areas with very high terrain in one area.
if we are coming for an approach for a runway which has an elevation of 100feet,and the MSA on the approach plate shows 9500feet,surely we are to descend and land,,my question is ,,arent we crossin the 9500 limit???since msa assures acceptable obstacle clearance of 1000non and 2000mountaineous,,??
They are not operational altitudes in the U.S., and they provide only 1,000 feet of vertical clearance, even in designated mountainous areas. Further, in U.S. RNAV IAPs they are not sectorized, which makes them of marginal value (at best) in areas with very high terrain in one area.
Join Date: Jul 2004
Location: Europe
Posts: 243
Likes: 0
Received 0 Likes
on
0 Posts
pilotsaab, in your case scenario you should be at the MEA or maybe a more favorable MORA when reaching the specified sector distance (most likely 25 nm) if not being radar vectored. If that MEA or MORA is higher than 9500 ft then you are in worse shape if what you want to do is to proceed directly outbound and do the reversal. The angle between your inbound feeder route and the outbound course will possibly prevent that course of action according to doc 8168. The approach will probably have either a DME arc or a racetrack overhead to lose altitude. Well there is always the divebomb technique 
Another dilema arises when you are shown 9000 ft MSA and 90 MORA but the TL level is below. Do you make adjustments for altimeter setting?
And fianlly the famous discussion that has been around on pprune on whether the MSA is for emg use only like on FAAland.
Another dilema arises when you are shown 9000 ft MSA and 90 MORA but the TL level is below. Do you make adjustments for altimeter setting?
And fianlly the famous discussion that has been around on pprune on whether the MSA is for emg use only like on FAAland.
