I love getting questions from readers and my favorite questions are the ones I don’t already know.  Such as the question I received lately from Jon regarding the max altitude on Tango routes:

Hi Paul. I’ve always wondered. On the Jacksonville sectional here in Florida we got a few T-Airways where the MAA is 15 000 feet. Now, the only reason I know of for a MAA restriction on an airway is because you can get several VORs on the same frequency etc, however, since this is a GPS airway, I don’t understand why an MAA would exist. Any ideas?

Well, this took a little digging but I found the answer! The first thing we need to do is understand why T-routes (pronounced “tango routes”) were established and how they help you.

Tango routes were established by the FAA at the request of AOPA in order to help pilots navigate around or through busy terminal areas.  RNAV (GPS) was utilized because using ground based NAVAIDS for these routes would have resulted in some seriously inefficient flying.  The FAA used RNAV to develop a point-to-point low altitude route system and designated this route structure, Tango Routes.  Tango routes enable the GPS equipped pilot to efficiently fly around or through busy terminal Class B and C areas.  They also help to reduce controller workload by being able to assign these routes to appropriately equipped pilots instead of having to provide manually intensive radar vectoring.  Here is an example of a t-route from an enroute chart (graphics courtsey of skyvector.com)

So now to answer our question, why do T-routes have a Maximum Authorized Altitude (MAA)? The reason is not because of radio reception or being able to get multiple frequencies but because of the airspace and the agency that controls the airspace above the route.

For instance, let’s take a look at our example from above.  In this case our MAA is 15,000 feet. Why?

Well, it might be for a couple reasons:

1) A T-route by definition in a low-altitude route.  It is designed to assist those pilots who are flying in some busy terminal areas who wish to stay out of the way.

2) The controlling agency above.  Because Tango routes are primarily terminal (in that they don’t involve the ARTCC centers) it might be that Jacksonville Center starts at 16,000 feet and in order to provide seperation to the airliner traffic above they limit the MAA on the T-route to 15,000.

3) The airspace above.  T-routes can also be designed to keep pilots out of a Class B airspace.  While that may not be the reason in our example, this can also be a limiting factor for the MAA on a T-route.

The important thing to remember is that to fly a t-route you will have to have an instrument rating, on a instrument flight plan and be IFR GPS equipped.   With all that control, all you really have to worry about is maintaining your assigned altitude.

One other thing to notice on a T-route is that because it is not dependent on receiveing traditional line-of-sight radio signals the MEA or Minimum Enroute Altitude is a lot lower.  The lower MEAs can be a significant benefit in route planning and avoidance of icing to keep you below the freezing level.

I hope this helps Jon and whether you are flying a V route, J route, Q route, Y route, or T route remember to…

Fly Safe!

Here’s a good question concerning logging of pilot time that I received from Don:

Can one log time as a safety pilot? If so, under what heading, eg, PIC, or a separate category “safety pilot“? Thanks.

First a quick review.

A “safety pilot” is a required flight crew member when another pilot is flying under simulated or actual instrument conditions in order to meet the IFR recency requirements of 14 CFR 61.57.  FAR 61.57 requires that in order to file and fly on a IFR flight plan you have to be instrument current, which means that within the past 6 months you have logged 6 approaches, holding and intercepting and tracking procedures.  If for some reason, those 6 months pass, the pilot has another six month grace period in which he can fly with a safety pilot under simulated instrument conditions in order to become fully instrument current again.  In simulated instrument conditions the pilot wears a view limiting device that blocks the pilot’s view of the outside world so that he can only see the instrument panel (we call them foggles).  This can present a problem for other airplanes as the flying pilot is unable to see where he is going!  The FAA found a solution to this problem by creating the safety pilot.  A safety pilot is simply that, someone who looks out for other airplanes (safety) while the other pilot is flying blind “under the hood”.

Instrument Training Glasses “Foggles”

So how do you log time flown as a safety pilot?

Because you are a required crew member when flying with a pilot under simulated instrument conditions the FAA allows you to log this time as SIC or second-in-command (61.51(g)).   If you agree to be the “acting” PIC you and the other pilot could both record the time as PIC but only when the other pilot is under the hood and the other pilot is the “sole manipulator of the flight controls.”   In order to be the “acting PIC” you will have to make sure that you meet the full PIC requirements for that flight and aircraft, which will include any necessary medical, category, class, type, recency and ratings requirements.

Don’t forget!  If you use a safety pilot to gain instrument currency the FAA requires that you record the name of the safety pilot in your logbook.

As always…fly safe!

I received an outstanding question this afternoon concerning instrument approach visibility minimums from Michael.  His question went something like this:

I’m looking at the RNAV (GPS) Z Runway 31 at McNary Field in Salem, Oregon (SLE) and I can’t make sense of the minimum visibility requirements of the approach.   Why is it that the visibility requirements for the LNAV only are so low?  On this particular approach the required visibility for the LNAV only is 2400 RVR or about a 1/2 mile.  That doesn’t make any sense!  I wouldn’t be able to descend from a MDA of 940 with only 1/2 mile of visibility!  Can you help shed some light on it?

Like I said mentioned before Michael, great question.  Let’s take a look at the RNAV Z RWY 31 approach into SLE.  For those who are interested, you can view a copy of the approach plate from EchoPlate:

Maybe at some point we’ll go over the terms and definitions of this approach plate a little more throughly, but for now, I’m going to try and just answer your question about the confusing visibility requirements.

Why are the visibility requirements so low for the MDA on the LNAV only approach?

The reason is the differences in the physical location of the Missed Approach Point (MAP) between the different approach types authorized for this approach.  Take a look at the MAP for the LNAV only approach and then compare it to the MAP for the LNAV/VNAV approach.   I have highlighted in red the locations of these two different MAPs in the illustration above.  For the LNAV only, the MAP is basically the start of the runway.  If you reach this MAP without having 2400 RVR AND you don’t meet the requirements of 14 CFR 91.175 then you must begin the missed approach procedure.  For the LPV approach and the LNAV/VNAV approach, the MAP corresponds with the DA which is most likely going to be physically further from the runway thus the higher visibility requirements.

Now you bring up an interesting point about the practicality of this approach.  Let’s say you are at a MDA of 940 and suddenly you have the airport environment and the required min. visibility, so you should “chop and drop” in right?  Well, let’s read 91.175 again.  14 CFR 91.175 says that in order to operate below MDA you have to be:

In a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers

So it may very well be that you have the required visibility before the MAP and you still have to execute a missed approach simply because you are not in a condition that you’ll be able to make it to the runway surface using safe and normal maneuvers.

I hope this clarifies things for you Michael.  If you have any other questions, feel free to comment on the this post and I’ll do my best to find an answer for you.

If anyone else has questions about the terms used in this explanation, feel free to ask me a question about which term you are confused about.

Thanks again for your question and ….

Fly Safe!