Sector Safe Altitude Question

[Tony747-400 44]

Hi Guys.

I know this isn’t really a PMDG related question but hoping one our knowledgeable people in the community can help.

If I’m on Radar Vectors from ATC and they ask me to descend below the SSA for the particular area I’m in, would a pilot in the real world query the instruction or follow it believing ATC know where they are directing you and would be clear of any obstacles? 

Thanks.

 

 

[downscc 1,327]

SSA? Social Security Administration?  Sorry, that TLA threw me. I've always seen it as MSA on charts and in discussions (FAA: Minimum Safe Altitude, ICAO: Minimum Sector Altitude).

I cannot speak to UK airspace, but in the US it would be unusual to be cleared by ATC lower than MSA except when within the TERPS defined cone that protects aircraft on arrival, in other words when vectored inside the defined constraints of the approach.  For example, MSA of 2000 and approach gives me  "turn right 060 descend to 1800 until established "  might be expected when the minimum outside of the FAF is 1800 (regardless of the MSA).  If you descend below the MSA in airspace not otherwise protected then alarms will go off in the ATC facility.

You always read back your clearance.... if the controller hears a readback that isn't right they will let you know (most the time).

[scandinavian13 5,192]

1 hour ago, Tony747-400 said:

If I’m on Radar Vectors from ATC and they ask me to descend below the SSA for the particular area I’m in, would a pilot in the real world query the instruction or follow it believing ATC know where they are directing you and would be clear of any obstacles? 

So, one thing a lot of VATSIM pilots don't understand is altitude applicability (not that all real pilots are much better - they just tend to second guess controllers less, though, I've found...but that tends to happen when something is a job versus something you do as a hobby).

SSA is only applicable when you have no other guidance. A vector is subject to the controller's MVA (minimum vectoring altitude), which the controller will maintain for you. When you get vectored off of your route, you will also receive an altitude on the first vector.

Pointing to the SSA to question a vectored altitude is like pointing to the SSA when flying the altitudes on an approach (which are lower than the SSA). The issue is that the SSA is to be used absent any other guidance. For example, you're on vectors and suspect you've lost radio contact: climb to SSA, re-establish yourself on a path of some sort (legs on an approach, for example), which have min altitudes that you can follow.

The main takeaway, I guess, is that you ALWAYS have an altitude requirement. The SSA simply provides you a basic, widely-applicable minimum altitude as a last resort. Just like your VFR Sectionals. There are big blue sector altitudes there. Does that mean you can't descend below those? Nope. Good info for a night flight if you don't have your exact position though? Yep.

9 minutes ago, downscc said:

SSA? Social Security Administration?  Sorry, that TLA threw me. I've always seen it as MSA on charts and in discussions (FAA: Minimum Safe Altitude, ICAO: Minimum Sector Altitude).

I cannot speak to UK airspace, but in the US it would be unusual to be cleared by ATC lower than MSA except when within the TERPS defined cone that protects aircraft on arrival, in other words when vectored inside the defined constraints of the approach.  For example, MSA of 2000 and approach gives me  "turn right 060 descend to 1800 until established "  might be expected when the minimum outside of the FAF is 1800 (regardless of the MSA).  If you descend below the MSA in airspace not otherwise protected then alarms will go off in the ATC facility.

You always read back your clearance.... if the controller hears a readback that isn't right they will let you know (most the time).

Not true, actually. Most MVAs are below the MSAs here in the States.

Example:

http://155.178.201.160/d-tpp/1802/00443ILD1.PDF

MVA is about 1800 on the south side, closer to the approach, from what I recall. I got some sass from a pilot on VATSIM one night.

...we all know how that ended.

EDIT: It may actually be as low as 1400 around the approach path, because I remember being able to get people below the glide slope intercept altitude even without being established...I could be remembering incorrectly, though.

[downscc 1,327]

1 minute ago, scandinavian13 said:

Most MVAs are below the MSAs here in the States.

Oh yeah, I knew all about MVA and then forgot everything I knew a couple of years ago.   I guess I was stretching it to reach out for terps to help me answer.

[BlueStar 323]

3 hours ago, Tony747-400 said:

f I’m on Radar Vectors from ATC and they ask me to descend below the SSA for the particular area I’m in, would a pilot in the real world query the instruction or follow it believing ATC know where they are directing you and would be clear of any obstacles? 

My answer will be "Maybe." Any time I'm not comfortable with the clearance that ATC is giving me, I'm going to ask.  If 'm not comfortable or unable to comply with the explanation I will tell ATC "Unable" and we go to plan "B".  I've had several telephone conversations once I got on the ground with ATC for clarification and the conversations were always cordial and professional.  Just like pilots, ATC makes mistakes.  

blaustern

[pilot87 12]

Under Australian flight rules, an Air Traffic Controller can descend an aircraft below an MVA by use of the term "visual" appended to the end of the instruction (i.e. "descend 2,100 visual"). They can only do it if the pilot has previously reported "visual" and terrain separation then becomes pilot responsibility. So in that circumstance it's always a good idea to have a quick look out of the window before reading it back to make sure you're happy to accept that clearance.

As a side note, I've got in the habit of checking the turn even before spinning the heading bug on a radar vector. ATC can't see where the clouds are and are usually accommodating to adjust a radar heading if required. Obviously thunderstorms are a different matter but summer fair weather cumulus will give you a bit of a kick under the wings as you go through them so I generally try to avoid them if I can. A smooth ride is as much a part of an airline pilot's job as getting the passengers to the destination safely!

[richjb2 195]

3 hours ago, Tony747-400 said:

Hi Guys.

I know this isn’t really a PMDG related question but hoping one our knowledgeable people in the community can help.

If I’m on Radar Vectors from ATC and they ask me to descend below the SSA for the particular area I’m in, would a pilot in the real world query the instruction or follow it believing ATC know where they are directing you and would be clear of any obstacles? 

Thanks.

 

 

Happens all the time. The SSA, what we in the U.S. call a MSA or TAA, may be higher than the Minimum Vectoring Altitude (MVA), used by Terminal ATC, or the Minimum IFR Altitude (MIA), used by Enroute ATC.   Using the MVA or MIA, controllers can and do assign altitudes below the MSA and TAA as well as below published altitudes on instrument approaches and STARs.  When they do this, the controller is responsible for terrain and obstacle clearance until the aircraft is established on the instrument procedures. Established is defined as on being on the lateral track of the procedure and at or above a published altitude on the procedure (ref. FAA Order 7110.65, para 4-8-1.b.2., Note 3). 

A controlled flight into terrain accident in 1974 involving TWA 514 was a watershed event that changed how ATC radar vectors are used and how ATC approach clearances are issued to arriving airplanes.  Here’s an excellent documentary on this crash:

 

Sad to say,we’re still having problems in this area.  In the past few months, we’ve had two near CFIT accidents, one involving a CRJ near Medford OR and another involving a B767 in Mexico because of clearances that seemingly cleared the airplane below published altitudes on the approach or airway, implying that the aircraft was above the MVA or MIA. Both airplanes were saved courtesy Mr. Don Bateman and his invention called EGPWS.

The moral of the story is that the pilot in command is ultimately responsible for safe terrain and obstacle clearance. Rule number one, don’t hit the rocks.     Maintain awareness of the published altitudes on the procedure. If an MVA chart is available (not in the US unfortunately, but working on that), maintain positional awareness based on that chart. If non-radar, never decend below a published altitude.  Query the controller if you’re in anyway unsure of whether the assigned altitude is safe.  Be weary of “at or above” altitude assignments where the at or above  altitude is lower than the published altitude or airway MEA.  In these instances, it is probably not wise to descend below the published altitude. 

Simply put, your question is still vexing pilots today.  

Thanks 

Rich Boll

Wichita KS. 

[berts 97]

On 2/18/2018 at 2:22 AM, richjb2 said:

Sad to say,we’re still having problems in this area.  In the past few months, we’ve had two near CFIT accidents, one involving a CRJ near Medford OR and another involving a B767 in Mexico because of clearances that seemingly cleared the airplane below published altitudes on the approach or airway, implying that the aircraft was above the MVA or MIA. Both airplanes were saved courtesy Mr. Don Bateman and his invention called EGPWS.

The moral of the story is that the pilot in command is ultimately responsible for safe terrain and obstacle clearance. Rule number one, don’t hit the rocks.     Maintain awareness of the published altitudes on the procedure.

I definitely agree with you on this one!  Sadly, one of the biggest ongoing issues for Flight Crew when flying below the Minimum Sector Safety Altitude continues to be avoiding controlled flight into terrain (CFIT).  In order to prevent CFIT accidents crews must carefully monitor the automatics and know exactly where they are at all times; and not just think they know exactly where they are (there is a big CRM difference here!).  The MSA or SSA shown on the arrival and departure plates is one factor and it is actually valid to a distance of 30nms from the airfield, although the plates are normally drawn to 25nms.

As you say, the introduction of (E)GPWS more than 30 years ago has reduced the number of CFIT accidents although it was not without its problems; such as false warnings and crews failing to react in time. For example, the original GPWS fitted to aircraft like the B744 did not protect against flight towards a vertical cliff or protect against slow descents in the landing configuration.

In the 6 year period from 1986 to 1991 there were no less than 44 CFIT accidents where the pilots were held responsible. Although the majority occurred in less developed countries where harsh economic conditions, poor weather and lack of modern navigation aids were contributory factors, in every case the outside visibility was limited by weather or darkness. However, what is perhaps more surprising about these accidents was the increase in the number involving high technology glass cockpits and the fact that the majority occurred on an ILS approach - and not as it might be reasonable to suppose - on a non-precision approach. (17 ILS, 13 VOR/DME, 9 LOC, 2 VOR, 1 NDB/DME, 2 Visual). It is therefore reasonable to assume that provided the pilots know where the ground is and can see it they will usually avoid crashing into Cumulo-granite!

You might also find interesting some of the other CFIT causal factors and brief recommendations from around this time, because they are just as valid today.

1) Altimeter setting errors – compounded by language problems.

2) Non-standard atmosphere anomalies – A B757 had a GPWS 50nm South of Seattle. The actual clearance was 1,200ft when it should have been 3,400ft. Better pilot/controller awareness of weather anomalies and other weather factors will help.

3) Minimal terrain clearances – off airways vectoring in lower airspace with too much trust placed on ATC. Improved procedures and worldwide terrain clearance standards will help. Simplified, uncluttered charts with the use of coloured terrain would result in improved situational awareness.

4) Pilot/ATC misunderstandings – of altitude clearances. Non-standard ATC, poor English or read-back errors are all issues. Better training of pilots and ATC controllers into the factors leading to CFIT accidents will reduce misunderstandings.

5) Navigation errors – incorrect selection, failure to check aids or improper procedures. These can be reduced by the use of GPS and improved cockpit displays with horizontal and vertical profiles of flightpath and terrain. Different forward looking sensors can see through different forms of precipitation – Improved Wx radar, infra-red, laser etc. will improve detection of CFIT as well as provide other flight safety improvements.

6) Lack of vertical situational awareness – altitude busts or errors contributed to 66% of CFIT accidents. A HUD would benefit pilots, especially if it had overlaid images of terrain and other obstacles.

7) Over-reliance on Flight Management Systems and the Autopilot by Flight Crew which often leads to unwarranted trust in the automatics. The multitude of modes and increased automation with each new aircraft type can sometimes lead to confusion and loss of situational awareness.

I suppose the important lesson in all of this is know your aircraft and its systems well, be vigilant even at the end of a long flight or duty day and don’t take anything - including Radar Vectors when at or below the MSA/SSA - for granted. Fortunately, today’s Enhanced GPWS provides much better protection through improved reliability, earlier terrain warning (including windshear warnings) and this all helps to enhance pilot situational awareness and therefore flight safety.  If you are a multi-crew pilot I'm sure many of us would like to know when was the last time you heard yourself or someone else on your Flight Deck say “What’s it doing now?” (but please don’t mention the use of the Thrust Button on the QOTS II B744 MCP!).

Bertie

[Skyflyer2018 25]

 

Kyle and everyone

 

This is a very interesting topic, I must admit you guys explain it a lot better than the official manuals should I say, would be good if it was incorporated into our OM (A) 😉.

 

James Barlow