Non-Precision Approaches Gone Bad

Non-Precision Approaches gone Bad 
Over the last six or nine months I have been occupied with a mildly covert campaign to get onto the top of the list of money earners among the Minneapolis Regional Carriers in the Econ2018 competition.  I have finally attained that status with a current  balance of $1,893,196.70. 

What is the Econ 2018 competition?  In the left-hand menu on our home page, click on Economics > Econ 2018 > Minneapolis- St. Paul Center > Regional Activities, to find out.  

Your second question is likely to be” who cares?”  And you have a point there.  At any rate, this post is likely to remove any covert aspect to the effort and I’ll likely fall back into the pack soon.  However, it was great for a while.  But that isn’t really the point of this post.  If you’re not familiar with the exercise: you create your own regional carrier (mine is Alak Air) and then choose from a list of assigned flights which is reset every twelve hours. These flights span Cat I thru Cat IV aircraft and specify the origin, destination, passenger and cargo loads.  Your flight is then supposed to be planned to result in the least cost and greatest revenue (greatest margin) through your flight planning, choice of aircraft and skillful execution of the flight.

These calculations are based on data provided by your SPAACARS filing and an “analytic” model, built by John Rogers and I about five years ago.  Since I built the computational engine for the model, I might be expected to have a leg up in the competition, but the model is pretty simple and so the process is pretty simple, use the lightest aircraft that can carry the assigned load and estimate the fuel required accurately.  Then fly the flight as smoothly and professionally as you can.  In the end, you make the most money with the long flights with the heaviest passenger and cargo loads. 

The fractional (%) margin can be large for smaller aircraft, but the absolute profit margin ($) will be largest for the heavier flights.  So, I had some personally imposed rules for how I conducted my flights:

(1) Do them in real (now) time and in real (now) weather
(2) do them in an aircraft I really enjoy flying – not just some crappy model that gets the job done. If you don’t enjoy flying the flight, why do it; the money isn’t real (sorry). 

So, since I started this project last Fall, and the flights either originate or terminate in Minneapolis, the days were short and the weather was bad.  I almost always wound-up landing in the dark, either in rain and/or snow.  Particularly so, since I couldn’t usually  get time to fly until it was 3 pm on the west coast and almost dark in the Midwest. 

I have several favorite Cat I and Cat II aircraft, but nothing I liked in Cat III, and my Cat IV and Cat V aircraft are too heavy for most of the available flights.  So, I started out picking flights which fit neatly into my (Cat II/III) ERJ-135 and ERJ-145 aircraft.  These are really good models, at almost the level you would see in a PMDG (B-738), Level D (B-763) or Aerosoft (A318/310/320) model.  But those aircraft are by-in-large way too big for the available flights. 

However, there are a couple of short-comings in the Feel-There ERJ models.  These are not short comings of the models, per se, but, I believe, limitations in the real-world aircraft capabilities.  These are: (1) No auto throttle, and (2) No RNAV capabilities.  The FMC and ND support the presentation of RNAV waypoints if they are part of your flight plan, but there is no way to couple the autopilot to the vertical part of a chosen RNAV approach. 

There are a least three distinct types of RNAV approaches and I have intended to write a brief tutorial on the topic, but that will have to wait until I get the time.  Suffice it to say that RNAV approaches do not rely on externally broadcast RF guidance signals (VOR, ILS, GS, etc.), but instead rely on navigation data generated or available in the aircraft from a combination of all available sources (Inertial, RF, GPS, etc.). 

If you routinely look at up-to-date approach charts for major and intermediate size airports you will see that many runways have only RNAV approaches and, in some rare cases, RNP approaches.  So, for example, when I was doing flights last winter that terminated in Minneapolis, I found that the real world winds frequently came from the SE and dictated use of Rwy 22, instead of the Rwy 12R/L, Rwy 30L/R pairs, routinely used in the summer.  The problem is that Rwy 22 has only LOC and RNAV approaches.  So, without RNAV capability, I was stuck flying the LOC approach in the dark and the rain, with no autothrottle and no precision vertical guidance.  I had a couple of pretty ugly landings, which cost me money and produced considerable frustration. 

I initially resorted to using VOR and Vs  modes on the autopilot and adjusting my rate of vertical descent to the value provided by the table on the approach chart, picked for the nominal value of the Vapp .  But, without an autotrottle, I ended up using some combination of pitch and throttle to stay on both the Vapp and Vs values.  This wound up being an unstable approach and I found it was just as well to turn off the autopilot and fly to approach visually using the VASI/PAPI, when I could see it.  Which takes me to the following Video:Which shows how a very similar problem led to near catastrophic results for an Air Canada Approach into Halifax in 2015 at night in bad weather without an ILS or RNAV on an A320.  This problem isn’t easy, even for highly trained professionals. 

Enjoy. Mike.