GOD POSITIONING SYSTEM

A priest recently mentioned this GPS thing to me, the God Positioning System.  While he wasn’t referring to the constellation of satellites, that seems appropriate for GPS since, for most people, the technology seems like some form of a divine miracle that provides you with your exact position on earth (or above it) at any point in time.  The reality is a little more scientific.  Here is a VERY brief explanation of the technology. 

GPS Overview:
Started in 1973 as a way to provide better navigational coverage, the Global Positioning System was developed by the US DoD to overcome limitations of previous navigation systems.  Have you ever seen the movie Hidden Figures?  The movie follows several important woman who worked as mathematicians during the space race.  One of those, Gladys West, was instrumental in the development of GPS.  Yes, the father of GPS was in fact, the mother.
 
Originally, the specification called for a minimum of 24 satellites with 4 satellites in each of the six orbital planes.  This is the typical number that is presented to aviation students when discussing GPS.  Over the years, that number has increased and the current system is organized in a 27 satellite configuration.  As of this writing, there are 31 satellites in orbit and another in “checkout.”  The original system became fully operational in 1995, although not without substantial limitations.  Some of you may remember when GPS seemed like a good idea but it was still pretty far off.  This was due to what was called Selective Availability.  It was meant to degrade the signal for civilians and provide only the military with the accuracy that we have come to know today.  As with most things in aviation, it took a tragic accident before GPS was determined to be a technology that should be available to everyone “for the common good,” to quote President Reagan.  In 1983, a Korean Air Lines 747 was shot down in Russian airspace because of an issue between their INS (Inertial Navigation System) and autopilot.  While it was released for civilian use after that, it wasn’t until 2000 that President Clinton signed a policy effectively removing Selective Availability from the GPS.  

So how does it work?
The basic theory of GPS is the use of time between the satellite time transmission and the reception of that signal by your GPS receiver.  Radio waves travel at a constant speed so the receiver simply does some simple mathematical equations to determine your position.  2+2=4 right?  The fundamental equation is actually quite simple, distance = rate x time.  GPS satellites broadcast time based on a HIGHLY accurate atomic clock at the speed of light.  Your GPS receiver will then receive that signal at some point in time.  That travel time is used in the calculation.  In order to get your 3D position, a minimum of 4 satellites is required.  Your GPS receiver is constantly listening for these signals in the 1,200 or 1,500 MHz frequency and making the appropriate calculations to determine your position on Earth.  Simple right?  Now that we have a very basic understanding of GPS, let’s look at the concept of WAAS and how that works in our aviation world.

WAAS Overview:
Present day GPS is far more advanced than the early days of the technology.  Some very smart people determined that we could utilize GPS in order to allow very precise location guidance in aircraft to fly instrument approach procedures.  In order to do that though, we need to be able to make corrections to the satellite signals.  In order to do this, there are a series of GPS receivers around North America whose sole purpose is to, well receive GPS signals from the various satellites.  Think of it like this:  A Garmin 430 sitting in a building somewhere just receiving signals.  These stations then take this collected information and send it off to a Wide-area Master Station, or WMS, to process the corrections.  This is done through standard terrestrially-based communication mediums.  Those master stations make the appropriate corrections and send those off to the uplink stations that then send corrected signal to the WAAS Satellites.
 
How does that corrected GPS information get back to you then?  An excellent question that many pilots incorrectly understand.  There are currently 3 satellites in geostationary orbit above the earth that receive these corrected signals.  These satellites then transmit the corrected signal data back down to your WAAS receiver to display corrected data.  All done in a matter of seconds, and all without any user intervention.
 
Practical Application:
Now that you have some basic knowledge about GPS, let’s put this into a scenario that you can apply to your next flight.  You are flying from San Diego to Monterey, CA.  The ILS is out of service so you decide that, since you have a Garmin 650 WAAS receiver, you will plan to fly the RNAV 10R approach since the winds favor that runway.  What minimums do you plan for?  Many pilots will look at the approach chart and determine that the LPV, since it has the lowest minima, is the way to go and brief it accordingly.  How do you know if you can fly that approach though?  Your Garmin 650 is continuously receiving signals from the WAAS satellites and if it is determined that the integrity of the signal will be compromised, the approach will degrade to the next lower minima (LNAV in this case) and you will see an annunciation on the unit.  This happens approximately 1 minute from the final approach fix.

Conclusion:
GPS is an amazing technology that will continue to be improved upon for the foreseeable future. It is important that as pilots, we understand the underlying technology not just because an examiner may ask it someday, but because our knowledge of these systems can directly affect the outcome of our flight.

You may also like...

Aviation General
System Administrator

Forget Best Glide

In light of the recent accidents, I thought it prudent to discuss engine failures. This article will not discuss the recent accidents, nor will it attempt to Monday-morning quarterback what could or should have been done differently.

Read More »

Leave a Comment

Plus One Flyers - Membership Agreement

Section A:  Agreement

I hereby certify that all the information on this membership form is true to the best of my knowledge.  I understand that any falsification shall be grounds for disqualification or forfeiture of my membership.  I have received, read, understand, and agree to abide by the Plus One Flyers, Inc. (the “Club”) Bylaws and Operational Rules.  In particular, I acknowledge that I have read and agree to be bound by Section 4.8 of the Bylaws, which states that I shall be responsible for any damages or abuse to an aircraft that I am using.  I also acknowledge that I have read and agree to be bound by Section 4.8.3 of the Bylaws, which provides that I shall not seek to hold Plus One Flyers, Inc. legally responsible for my acts while operating a Club aircraft which results in damages or injuries, whether to myself or others. I further acknowledge that I have read and agree to be bound by Article VII of the Bylaws, which provides that I shall be fiscally responsible for my dues, timely flight payments and any collection fees.

In the event that any damages are assessed against the Club as a result of my acts or negligence, I shall be solely responsible for the payment of those damages and for any legal fees or costs incurred by the Club in defending itself.  As set forth by Article VII in the Plus One Flyers Inc. Bylaws, each member, and their heirs, successors, personal representative and assigns, release, acquit, and covenant not to sue, and  shall indemnify, defend, and hold harmless the Club, its officers, directors, agents and employees for any liability, losses, or damages that I or the Club may suffer as a result of an act by, or negligence of, the member while operating a Club aircraft. Each member must acknowledge and agree that he or she is accepting and using any and all Club aircraft in a used, “as is” condition and that the Club does not and has not repaired, reconditioned, or maintained any Club aircraft.  Each member must agree to assume all risks, and assumes full responsibility for risk of bodily injury, death or property damage associated with any Club aircraft and not to seek to hold the Club legally responsible for any such defects in Club aircraft before being allowed to use and fly Club aircraft.

Finally, I understand, should I resign from the Club, my resignation notice (form) must be given in writing at least thirty (30) days prior to leaving the Club and that I will return my club key(s) on or before my resignation date, which is effective the 1st day of the next month following that 30 day period. Membership remains effective until terminated under the terms of this Agreement.

I also agree and understand that:

A.     I will not allow non-members, whether pilots or not, to operate Plus One Flyers Aircraft because they are not insured through Plus One Flyers.  All flight instructors instructing in Club Aircraft must be members of Plus One Flyers, Inc., and be authorized by the club’s Safety Program.

B.     I will not operate Club Aircraft if my FAA medical or Flight Review is not current.

C.     I will not operate Club Aircraft for hire, either under Part 91 or Part 135 of the FAR’s, because the Club’s insurance does not cover such operations.

D.     I, alone, am personally and financially responsible if I participate in any uninsured operations of Club Aircraft.

E.     I will maintain and promptly notify the Club of any changes to my telephone numbers, billing address, email, and credit/debit card(s) information by updating this information myself in Schedule Master.          Initial here_________

F.     I will promptly notify Plus One Flyers if I am involved in an aircraft accident, even if it is not a Plus One Flyers Aircraft.

G.     I authorize my bank or credit/debit card company/companies to make monthly or yearly (as specified in Section B) payments to Plus One Flyers, Inc. and post it to my account.                               

H.     I authorize my bank or credit/debit card company/companies to make payments for possible collections for errors or non-payments of flights to Plus One Flyers, Inc. and post it to my account.

I will promptly and regularly submit updated copies of my Medical Certificate and Flight Review to the Club’s Membership Officer.

 

Section B:  Automatic Payment and Credit/Debit Card(s) Guarantee

The credit/debit card(s) you provide on this form and/or in Schedule Master serve as your payment guarantee and is required in your Schedule Master Membership account to enable and maintain your airplane scheduling privileges. Plus One Flyers will charge your card(s) and email you an invoice for any payment shortages.  Any dispute regarding a charge can be handled by the Club Membership Officer.  If an error results in an amount owed you, Plus One Flyers will credit your Schedule Master account balance unless you request a refund check.
 

Membership Dues are $29.00 monthly, charged to your credit/debit card(s) or if available, against a pre-paid credit balance.  Paying Annual Dues means you maintain a pre-paid credit balance that is reduced by $31.00 monthly until zero and if you elect to continue to pay Annual dues, you are responsible for pre-paying the appropriate amount each year.  There is a $129.50 initiation fee for new members and renewing members, except for those members renewing while serving active duty in U.S. Armed Services.  If there is a change in dues you will receive a thirty day notice by email and a message will be posted in Schedule Master. Your account will be charged on the 1st of every month if you choose the monthly option.  An email invoice will be sent to you every month.  It is your responsibility to view your invoices/account to verify that your payment has been made.  You are responsible for ensuring your card(s) remains current and that if it expires or your billing address changes you alone are responsible for updating that information in Schedule Master.  If your bill has not been paid your scheduling privileges will be automatically suspended until it is paid.  If three consecutive dues invoices remain unpaid your membership will automatically terminate and a $99.00 initiation fee plus the past due balance will be required to reinstate your membership.  If you take no action your account may be sent to a collection agency.
 

Keep your billing address and email address and card(s) current in your Schedule Master Membership Account. Plus One Flyers is not responsible for ensuring your email system allows Schedule Master or other Club emails to reach you.  You will receive an automatic email one month prior to the expiration of your card in Schedule Master.  Plus One Flyers is a PCI-DSS-compliant e-commerce and POS credit card processing merchant.  See the Club’s Privacy Policy for more about how we protect your private information.                                                                                              

Scroll to Top