Military Aviation A forum for the professionals who fly military hardware. Also for the backroom boys and girls who support the flying and maintain the equipment, and without whom nothing would ever leave the ground. All armies, navies and air forces of the world equally welcome here.

Descents to VMC

Old 16th Dec 2021, 14:31
  #1 (permalink)  
Thread Starter
Join Date: Dec 2021
Location: Shropshire
Posts: 1
Descents to VMC

Canvassing pilotís thoughts regarding descents to get VMC below from an ATC perspective.

If youíve planned a descent to VMC would you expect;

1. An ATC unit to vector you into an area of better theoretical base of solid radar cover straight away, taking you off your planned track but allowing to you to descend as low as possible iaw the units Terrain Safe Level?
2. A descent initially to the units theoretical base of solid radar cover above the units Terrain Safe Level and only then, if still IMC and wanting further descent, to be issued a with a turn to remain in theoretical base of solid cover taking you off your planned track?

The above two may seem like semantics but Iím trying to establish ďbest practiceĒ based upon Mil pilots requirements/experience.

One further question, if you were still IMC having been issued a descent to the theoretical base of solid radar cover and wanting further descent would you be happy to maintain your planned track and be issued a descent to the units Terrain Safe Level and accept reduced traffic information from all around with your deconfliction service as you descend?

In all these scenarios above would you like/expect the controller to ascertain your requirements rather than imposing?

Any replies would be much appreciated. Thanks
Benbow1 is offline  
Old 16th Dec 2021, 21:35
  #2 (permalink)  
Join Date: Nov 2006
Location: USA
Posts: 171
Its been a while for me, but if memory serves me correctly, you can descend IMC all the way down to what ever the SALT is for your proximity. I dont think you could descend LL for VMC unless you are on a recognized TAP approach to an airfield.
1771 DELETE is offline  
Old 17th Dec 2021, 09:42
  #3 (permalink)  
Join Date: Nov 2005
Location: River Thames & Surrey
Age: 73
Posts: 9,355
Take a look at published SMACs (Surveillance Minimum Altitude Charts) for radar vectored descents.
chevvron is offline  
Old 17th Dec 2021, 11:48
  #4 (permalink)  
Join Date: May 2002
Location: Scotland
Posts: 613
Somewhere in prune you will find an account of the court martial of a Leuchars controller involved in the loss of two F15s descending IMC. All these issues are extensively explored.
Timelord is online now  
Old 17th Dec 2021, 16:19
  #5 (permalink)  
Join Date: Nov 2007
Location: Highlands
Posts: 85
For those unaware of the above Court Martial in 2003, the controller was acquitted of charges of causing the deaths of the 2 aircrew and professional negligence.
BlackIsle is offline  
Old 17th Dec 2021, 19:14
  #6 (permalink)  
Join Date: Apr 2009
Location: Wherever it is this month
Posts: 1,666

I don't believe the Ben Macdui case makes any reference to the concept of 'theoretical base of solid radar cover'. It hinged entirely on the minimum terrain safe levels and the division of responsibility between pilot and controller for avoiding the ground. None of the scenarios posited by the OP involve descent below minimum terrain safe levels; the variable he/she wishes to explore appears to be the quality of traffic information required during an IMC descent (less than solid radar cover = less than complete traffic information). We know that midair collision risk has been a key focus for duty holders in recent years so I'd be surprised if there isn't already some official guidance material available.

My 2p worth: if timing was critical and I was expecting an IMC descent I would plan my route through an area of low terrain safe level with good radar coverage if at all possible. Inclusion of radar vectoring charts and radar coverage plots in flight publications is therefore extremely valuable. Whether I would re-route to stay in good radar coverage rather depends on the circumstances. In general, I tend toward the view that remaining on track and descending below solid radar cover is a better option than rerouting, adopting 'big sky theory' (which after all is the regulatory basis for the UK's Class G airspace: if the risk or consequence of collision is higher in a particular location then for God's sake do what the rest of the world does and define some airspace other than Class G, rather than introducing non-enforceable local procedures!). TCAS mitigates the risk substantially, but I would be more circumspect if over a glider site without FLARM. I would be even more circumspect if flying air cadets on an AEF. On reflection I think 'best practice' is for aircraft operators to determine based on their particular requirements and risks. There are probably too many variables in this for controllers to do anything other than respond to pilot requests.
Easy Street is offline  
Old 17th Dec 2021, 19:31
  #7 (permalink)  
Join Date: Mar 2006
Location: SW
Posts: 202
If you want a descent to VMC under rdr you want to go straight down to the minimum the controller can provide.
An idea of the cloudbase will determine whether it's worth vectoring to a lower area. Proximity to significant terrain is also an issue because in some areas that vector could result in several 1000' difference and in flat areas only a few 100'.
Reduced traffic shouldn't be an issue unless there is someone else IMC below MSA/SALT in your area not talking to anyone.
Hope this is useful.
switch_on_lofty is offline  
Old 17th Dec 2021, 23:36
  #8 (permalink)  

Avoid imitations
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 13,727
There is little point in being vectored well off track to descend to VMC if you cannot subsequently continue under VFR to your intended destination.

However, if you are descending to find VMC to continue to a diversion, that’s a different ballgame.

ShyTorque is online now  
Old 18th Dec 2021, 01:47
  #9 (permalink)  
Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 3,786
Sometimes a descent, off-track and over water, to VMC with a subsequent helicopter VFR approach to the controlled airfield is preferred to being held (because you are slow) or even being given the boot (happened once) while the RPT jets make instrument approaches. Did it many times.
Ascend Charlie is offline  
Old 20th Dec 2021, 20:10
  #10 (permalink)  
Join Date: Mar 2005
Location: Wyoming
Posts: 360
IIMC incident 2016, Florida (good outcome)

Food for thought, as reported by the pilot, (2016)

He was doing HAA workover in Florida, EC135 (non-IFR program) but he was current as an IFR pilot. Night VFR flight and went IMC, broke out after a few minutes, encountered second IMC and declared emergency with ATC. He requested vectors to VFR and ATC responded, "Do what you need to do to maintain VFR" ATC did ask him if he had visual with the antenna at 12 which he did not, and they gave him a vector away from the tower. He already set up the autopilot during the second IMC and began a climb to attempt to get above the cloud deck, which he did not break out and leveled off at 5000 msl.

Hearing several aircraft reporting to ATC they broke out at 1500 msl, he began a decent. He broke out at 1500 and advised ATC he was VFR and returning to base.

Some takeaways from the incident after reading his report and discussion with him.
He was proficient/current IFR pilot, so he set up the autopilot and was not concerned with the ATC response.
Leveled off at 5000 hemispheric but didn't think about possible conflict with an aircraft on an IFR flight plan.
He felt that he knew where he was (Garmin moving map) when he began the decent, not 100% sure of possible obstacles and he did not announce to ATC he was descending.
He did not observe his rate of decent (2200 FPM), determined by the Safety department review of aircraft system alerts.

The company training program and from day 1 as a pilot during IIMC training the steps are the same, Declare an Emergency, Request vectors to VFR, Request vectors to an Instrument approach. All of which the instructor accommodates, the pilot didn't question the ATC response because he felt ok with his skill set.

We ran this same situation during sim periods and flight training in which ATC (Instructor) gave the same instruction "Do what you need to do to maintain VFR" after declaring the IIMC emergency. 75% of the pilots pushed back to ATC regarding and emergency and assistance, the other 25% did not question ATC and "winged it".

The Director of Operations presented the report to the FAA asking to inquiry with ATC about the incident. An official response regarding ATC was never presented back to the instructor staff.

havoc is offline  
Old 20th Dec 2021, 21:03
  #11 (permalink)  
Join Date: Aug 2008
Location: The land of the green and grey
Posts: 41
If talking Helictopters, then I'd descend to SALT before requesting vectors to/procedural approach to overshoot VFR below the cloud. From my local unit I know their Safe Terrain Height is actually very high (Normally get a "responsible for own Terrain Clearance" either due to performance or sector that we are in). Depending on the tasking and location I would probably take a diversion as we aren't allowed to trust our GPS (When will we see the RNAV/PBN clearance?) Failing that head out to sea and descend down to 500' or a bit lower if you've got your own RADAR.

The problem with planning to stay at a units theoretical base of solid cover is that it changes so can't really be relied upon, if you have lumpy gorund then it's also going to vary depending on which sector you are in so makes planning difficult.

I've watched pilots try to descend using vectors from ATC and watched horrified as people have tried to squeeze out the last few feet below Safe Terrain Coverage or worse just get themselves into more of a pickle.
matelo99 is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.