MAP identification if the primary nav source is lost.

[R. Lee Buechler]

Let's say you are past the FAF on a VOR (or even a very unlikely NDB) approach which uses a navaid on the field.  No timing information from FAF to MAP is provided because the nav aid is the MAP.  What do you do if the navaid goes off the air (and, of course, you are IMC without radar assistance at this point in the flight)?  Further, let's say the published missed includes a climbing turn.  It's not rocket science to understand that an immediate climb is called for.  When do you begin the turn?

Subject of some hangar talk a couple of days ago and nobody had the answer.  And nobody had trained for this.  It appears that busted approach remedies are mostly about weather and loss of GS, but not about loss of primary signal.  And, remember, you must be able to continuously identify the navaid on final -- so if the ID feature fails, you are technically required to fly the missed.

Just askin'. 

[Richard Druschel]

Lee, Good question for thought. Even though, as you mentioned, there is no time specified I still like to have a ballpark idea of the time it is going to take me to get to the MAP, ie at 120 kts (two miles per minute) and a distance of say 5 miles from FAF to MAP, I should see about 2.5 minutes. If I had a GPS sitting there doing nothing I would have put the approach on it for backup reference. I could in that case use the MAP shown on the GPS.

In any event, once I saw that the approach navaid had failed, I would initiate an immediate climb. Then figure out the turn point.

In your example, how do you know the navaid failed and not the radio itself. In flying corporate jets both nav radios were tuned to the approach frequency. If the number one radio failed we could rely on the number two unit. I still use this technique with my F33A.

When flying IFR use every tool at your disposal to back up the primary units.
Dick

[R. Lee Buechler]

Thanks, Dick.  Good answer.  Most of us have dual Navs with a panel GPS that includes approaches.  Many have a 2nd GPS.  In my case, the GPS is a 530W which includes a Nav.  The 530 nav screen shows my progress through the approach, no matter what kind it is.  Makes it straightforward to confirm MAP arrival.  For those with portables, such units will generally not show approach paths, but will show all navaids which which means the MAPS we are considering are therefore shown.  So these folks also have a solution.  More troublesome if one has an earlier GPS without a graphical viewscreen.  I'll share your comment with my friends..............

[Thomas Pelz]

Lee,

One of the things I would avoid doing is begin the turn too early.   

Looking at the approach plate, you know what your minimum safe altitude is in any quadrant.

If you are on the VOR or LOC approach and the ground equipment craps out, then I would immediately abort and begin my climb to safe altitude before I would begin my turn.

Of course, each approach and location is different.  So, as you have pointed out, positional awareness that is granted to us by the moving map displays many of us have in our cockpits, enables us to make a more informed decision.   

Along this line of reasoning, I believe that each pilot should have a minimum descent altitude (AGL) that he/she will descend to for any approach.   My personal minimums are 500 feet AGL, no matter what the legal minimums are.  IF I were flying into some challenging mountain areas, I might want my minimums a whole lot higher.   

My attitude is (if there exists no emergency) I DO NOT have to land.   I try to maintain a minimum fuel reserve of two hours.  That way, I can travel at least 300 NM before I run out of gas.  With the current METARS available during flight, I can often make my no go decision without even trying to "look see".   At the price of gas now, it often is easier to make an approach to a VFR airport, sit out the weather (or spend the night) and continue on in the morning with full fuel.

Tom 

[Richard Reeves]

Lee,

The situation you are referring to would be a non precision approach.  Generally, I would just start flying the miss, remember that non precision approaches are designed so that you can drop to the step down altitudes immediately after crossing the fix where the step down is, and you should have at least a mile on either side as an approach corridor.  The only caveat I would have is with respect to a turn back (if there is one), is that if the instrument failure occurred just after a step down, and I would climb to at least the lower of the missed approach altitude and the previous step down altitude before turning back.

Rick
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