Return-Path: Sender: To: lml@lancaironline.net Date: Sat, 12 Nov 2005 17:04:40 -0500 Message-ID: X-Original-Return-Path: Received: from imo-m27.mx.aol.com ([64.12.137.8] verified) by logan.com (CommuniGate Pro SMTP 5.0.1) with ESMTP id 828667 for lml@lancaironline.net; Sat, 12 Nov 2005 12:09:41 -0500 Received-SPF: pass receiver=logan.com; client-ip=64.12.137.8; envelope-from=JIMRHER@aol.com Received: from JIMRHER@aol.com by imo-m27.mx.aol.com (mail_out_v38_r6.3.) id q.249.f68494 (4328) for ; Sat, 12 Nov 2005 12:08:50 -0500 (EST) From: JIMRHER@aol.com X-Original-Message-ID: <249.f68494.30a77ba2@aol.com> X-Original-Date: Sat, 12 Nov 2005 12:08:50 EST Subject: Navigating in the IFR system in an experimental aircraft X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1131815330" X-Mailer: 9.0 SE for Windows sub 5021 X-Spam-Flag: NO -------------------------------1131815330 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en Here is a must read article, for us IFR pilots, just published in Kitplanes= =20 and was written by my friend Keith Thomassen. He also teaches classes for=20 REALLY using the 530/430's, 480, Chelton EFIS. Here is his web address for=20= the=20 classes if interested; _http://www.avionicswest.com/_ (http://www.avionicswest.com/)=20 I'm just installing a 480 and have the EFIS so I will be taking the class =20 soon. Jim Hergert L4P N6XE, 350 hrs What is required for navigating in the IFR system in an experimental =20 aircraft? This question stimulates lots of opinion and much =20 disagreement, even if you=E2=80=99re asking FAA representatives. That=E2= =80=99s =20 because there is room for =E2=80=9Cinterpretation=E2=80=9D in the rules. Wh= at are =20 those rules and how are they to be interpreted? Let=E2=80=99s reason togeth= er =20 starting with what is written. The rules for flying IFR are given in Part 91.205 for =E2=80=9Cpowered civi= l=20 aircraft with standard category US airworthiness certificates=E2=80=9D. Th= ese=20 are not just the rules, they are in fact permission to fly IFR if you=20 satisfy them (and are rated and current). So they are both necessary=20 and sufficient conditions for IFR flight in certified aircraft. For experimental aircraft your Operating Limitations, issued after the=20 FAA inspection and licensing of your aircraft, determine whether you=20 can fly at night, do aerobatics, or use the aircraft in the IFR system.=20 For IFR approval there will be a statement in those Limitations making=20 Part 91.205 applicable to you. The requirements of Part 91.205 can be lumped into two groups; 1) a=20 list of instruments that include those for day VFR, night, and=20 additions for IFR, and 2) the statement that you must have =E2=80=9Ctwo-way= =20 radio communications system and navigational equipment appropriate to=20 the ground facilities to be used=E2=80=9D. Most of the instruments are self-explanatory, like airspeed, compass,=20 altimeter, clock, etc., but there is some confusion on gyro instruments=20 (rate-of-turn, pitch and bank, directional indicator) now that solid=20 state AHRS devices are being used. The Experimental Aircraft =20 Association (EAA) has worked with the FAA Small Airplane Directorate to =20 resolve that issue; if it performs the function it is acceptable. A more confusing issue that is addressed here concerns GPS units for=20 IFR flight. There are several FAA documents on using GPS, such as the =20 navigation chapter in the AIM or the circular on GPS (AC20-138a). But =20 advisory circulars are just that, and are not regulatory. So let=E2=80=99s=20= =20 explore the use of GPS for IFR flight. First, as the EAA also concludes, the equipment does not have to be=20 certified. But they concluded in their written summary that the=20 required navigational equipment statement in 91.205 says that you can=E2= =80=99t=20 use GPS for your primary navigation system because it is not=20 ground-based. They conclude that your primary system must be ground=20 based (VOR=E2=80=99s), but that is also true if you installed a certified G= PS=20 under TSO 129c, so more discussion is needed there. Also, a GPS=20 certified under TSO 146 does allow a GPS to be your primary navigation=20 system. Let me clarify these points in some detail. If you had a Garmin 1000 (or a King KLN94, or Garmin 430/530) it cannot=20 be used for your primary navigation system. These are all certified=20 under TSO 129c, and as such they are certified for supplemental =20 navigation. That=E2=80=99s because the FAA has integrity criteria for =20 discontinuing their use in IFR flight, and the requirement for an =20 integrity monitoring system that can warn you not to use the GPS for =20 navigation. The Receiver Autonomous Integrity Measurement (RAIM) =20 system must warn you if you don=E2=80=99t meet the RAIM requirements for you= r =20 phase of flight =E2=80=93 2 nm while enroute, 1 nm in terminal areas (within= 30 =20 nm of your departing or arrival airport, where you might do a SID,=20 STAR, or missed approach), and 0.3 nm in the approach phase (final to =20 missed). Clearly, the reasoning goes, if it might be rendered unusable it can=20 only be certified for supplemental navigation. That=E2=80=99s why such a=20 receiver cannot be used at an alternate airport where there is no other=20 type of approach (than GPS). If there is one, of course, you can do=20 the GPS approach there. Supplemental use is not all that restrictive in that you don=E2=80=99t have= to=20 be navigating by VOR and DME if your GPS is within RAIM limits. You=20 must, however, be able to make that flight with the GPS turned off. =20 All ground navaids must be operational (don=E2=80=99t file a route over an=20 inoperative VOR), and your VOR receivers must be operational. Of=20 course, you wouldn=E2=80=99t file GPS-Direct over routes that require RNAV=20 equipment (long distances in areas of sparse navaids), unless you have=20 RNAV equipment. While this is commonly done, ask yourself what you=E2=80= =99d=20 do if you had a RAIM failure on that segment. So, how about your non-certified GPS? If it has the functional=20 requirements of the certified equipment, you should (I say) be able to=20 use it. If questioned, the burden of proof is on you that you have met=20 the =E2=80=9Cnavigational equipment=E2=80=9D requirement of 91.205. The FA= A could use=20 FAA policy or applicable court decisions to decide otherwise, but here=20 things are grey. At least you should ensure that your unit does the=20 integrity monitoring that is at the heart of the TSO 129c requirements=20 and limitations. Then, you should use it as supplemental to your=20 primary system in the sense I just described. If you believe your unit meets these standards, is it ok to do GPS (and=20 overlay) approaches with it? If it contains the latest Nav data base=20 and it does the RAIM check internally before you execute it, I say yes.=20 The only difference between enroute/terminal and approach phases is=20 the more stringent RAIM requirement or the latter. But the world of aviation has evolved, and now there are receivers=20 certified under TSO 146, which requires using the WAAS system. If you=20 never wanted to do NDB, VOR, or ILS approaches, you could fly with this=20 GPS and a COM transceiver for all your flying, and save the money=20 needed for a DME, ADF, VOR, and LOC/GS receivers. This TSO has tougher=20 requirements on position accuracy that can only be met by adding WAAS=20 error correction to your raw GPS position solutions. Ground stations around the U.S. receive raw GPS position solutions and=20 send their 3D position error (they know where they really are) to=20 geosynchronous satellites in the east and west. Your WAAS enabled GPS=20 receives the errors from those satellites and, by interpolation using=20 errors at ground stations near you, adds a 3D correction. The=20 WAAS-corrected solution is claimed to be accurate to a meter horizontal=20 and two meters vertical (best case, I suspect). The raw GPS solutions have an accuracy affected by the dilution of=20 precision (DOP), which comes from poor geometry (all the satellites=20 lumped close together gives a lousy solution). As in any triangulation=20 scheme, horizontal position is best measured if stations are on both=20 sides of you (on the horizon left and right). Since vertical position=20 cannot be determined by satellites above and below you (the earth is in=20 the way) your raw vertical position is not nearly as accurate as the =20 horizontal. WAAS corrections largely fix that, so WAAS is critical to =20 vertical operations, such as using GPS altitude for terrain avoidance =20 (TAWS systems) or doing GPS vertical approaches. There are other large =20 errors due to the slowing down of the GPS signal through the ionosphere =20 and atmosphere (light slows down a factor of about 9 in water), and =20 these too are corrected in real time since the ground stations =20 experience the same extra delays. The Chelton Flight Systems are certified under TSO 146, so they can be=20 used for primary navigaton. So if you purchase the experimental=20 Chelton system, can it be used for primary navigation? Since the FAA=20 also imposes integrity monitoring on 146 units, it must give integrity=20 warnings as specified by that TSO. These include measuring the=20 horizontal and vertical protection limits (HPL, VPL), which you will=20 find on the satellite page of the Garmin 480, the only other GPS =20 certified under TSO 146. The certified Cheton gives the required =20 integrity warnings through its Free Flight GPS engine and software, so =20 if your experimental Chelton uses that GPS engine (this is an option on =20 their Pro system) those warnings are given and (I believe) this =20 satisfies the FAA intent. But the Chelton is currently certified for LNAV operations only, so=20 LNAV/VNAV and LPV approaches are verboten. Why? If you are going to=20 track a vertical GPS course to LPV minimums, for example, an FAA=20 requirement in TSO 146 is to determine your position 5 times per=20 second, not once as in all TSO 129 receivers and the Chelton. But=20 there is more. The LNAV/VNAV and LPV approaches are called Approaches with Precision=20 Vertical (APV). This means that, in software, the full scale CDI=20 deflection is reduced as you go down the glideslope much as both ILS=20 localizer and glideslope courses reduce the full scale deflection as=20 you proceed to the runway. The increased sensitivity keeps you in a=20 smaller and smaller box, and you must abort if you can=E2=80=99t keep the=20 needles off the pegs. So here is another set of requirements on refresh times and CDI=20 sensitivity. By the way, there is also an increased sensitivity=20 horizontally for LPV approaches, but not for LNAV/VNAV, hence the=20 former have the lowest minimums and visibilities (generally). At the=20 moment, the only GPS available, certified or not, that can meet these=20 requirements is the Garmin 480, so at the moment it is a moot point and=20 the real issue today is whether your WAAS GPS can be used for primary=20 IFR navigation. The requirements extracted here from TSO 129c or 146 are by no means a=20 complete set, and it=E2=80=99s not clear whether you need to meet others no= t=20 listed. There are requirements on environmental, software, data, and=20 manuals for example, but I believe as for gyros, the main issues are=20 functionality (which includes fault detection). As the pilot and=20 manufacturer of your aircraft however, the burden of proof is on you to=20 determine if you meet the 91.205 requirements for IFR flight. Finally, only you can decide what equipment is sufficient for your type=20 of flying. Redundancy is important, and everyone will have a different=20 comfort level with various backup options. But I hope this gives more=20 insight into using one of the many new GPS systems available to the=20 experimental=20 Keith Thomassen -------------------------------1131815330 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en
Here is a must read article, for us IFR pilots, just publishe= d in=20 Kitplanes and was written by my friend Keith Thomassen. He also teaches= =20 classes for REALLY using the 530/430's, 480, Chelton EFIS. Here is his=20= web=20 address for the classes if interested;
http://www.avionicswest.com/
I'm just installing a 480 and have the EFIS so I will be taking the cla= ss=20 soon.
Jim Hergert
L4P N6XE, 350 hrs
 
 
What is required for navigating in the IFR system in an experimental=20
aircraft?  This question stimulates lots of opinion and much=20
disagreement, even if you=E2=80=99re asking FAA representatives.  T= hat=E2=80=99s=20
because there is room for =E2=80=9Cinterpretation=E2=80=9D in the rules.=   What are=20
those rules and how are they to be interpreted?  Let=E2=80=99s reas= on together=20
starting with what is written.

The rules for flying IFR are given= in=20 Part 91.205 for =E2=80=9Cpowered civil
aircraft with standard category U= S=20 airworthiness certificates=E2=80=9D.  These
are not just the rules,= they are in=20 fact permission to fly IFR if you
satisfy them (and are rated and=20 current).  So they are both necessary
and sufficient conditions for= IFR=20 flight in certified aircraft.

For experimental aircraft your Operatin= g=20 Limitations, issued after the
FAA inspection and licensing of your aircr= aft,=20 determine whether you
can fly at night, do aerobatics, or use the aircra= ft=20 in the IFR system.
  For IFR approval there will be a statement in=20 those Limitations making
Part 91.205 applicable to you.

The=20 requirements of Part 91.205 can be lumped into two groups; 1) a
list of=20 instruments that include those for day VFR, night, and
additions for IFR= ,=20 and 2) the statement that you must have =E2=80=9Ctwo-way
radio communica= tions system=20 and navigational equipment appropriate to
the ground facilities to be=20 used=E2=80=9D.

Most of the instruments are self-explanatory, like air= speed,=20 compass,
altimeter, clock, etc., but there is some confusion on gyro=20 instruments
(rate-of-turn, pitch and bank, directional indicator) now th= at=20 solid
state AHRS devices are being used.  The Experimental Aircraft= =20
Association (EAA) has worked with the FAA Small Airplane Directorate to=20
resolve that issue; if it performs the function it is acceptable.
A=20 more confusing issue that is addressed here concerns GPS units for
IFR=20 flight.  There are several FAA documents on using GPS, such as the=20
navigation chapter in the AIM or the circular on GPS (AC20-138a). =20= But=20
advisory circulars are just that, and are not regulatory.  So let= =E2=80=99s=20
explore the use of GPS for IFR flight.

First, as the EAA also=20 concludes, the equipment does not have to be
certified.  But they=20 concluded in their written summary that the
required navigational equipm= ent=20 statement in 91.205 says that you can=E2=80=99t
use GPS for your primary= navigation=20 system because it is not
ground-based.  They conclude that your pri= mary=20 system must be ground
based (VOR=E2=80=99s), but that is also true if yo= u installed=20 a certified GPS
under TSO 129c, so more discussion is needed there. = ;=20 Also, a GPS
certified under TSO 146 does allow a GPS to be your primary=20 navigation
system.  Let me clarify these points in some=20 detail.

If you had a Garmin 1000 (or a King KLN94, or Garmin 430/530)= it=20 cannot
be used for your primary navigation system.  These are all=20 certified
under TSO 129c, and as such they are certified for supplementa= l=20
navigation.  That=E2=80=99s because the FAA has integrity criteria=20= for=20
discontinuing their use in IFR flight, and the requirement for an=20
integrity monitoring system that can warn you not to use the GPS for=20
navigation.  The Receiver Autonomous Integrity Measurement (RAIM)=20
system must warn you if you don=E2=80=99t meet the RAIM requirements for= your=20
phase of flight =E2=80=93 2 nm while enroute, 1 nm in terminal areas (wi= thin 30=20
nm of your departing or arrival airport, where you might do a SID,
S= TAR,=20 or missed approach), and 0.3 nm in the approach phase (final to=20
missed).

Clearly, the reasoning goes, if it might be rendered=20 unusable it can
only be certified for supplemental navigation.  Tha= t=E2=80=99s=20 why such a
receiver cannot be used at an alternate airport where there i= s no=20 other
type of approach (than GPS).  If there is one, of course, you= can=20 do
the GPS approach there.

Supplemental use is not all that=20 restrictive in that you don=E2=80=99t have to
be navigating by VOR and D= ME if your=20 GPS is within RAIM limits.  You
must, however, be able to make that= =20 flight with the GPS turned off. 
All ground navaids must be operati= onal=20 (don=E2=80=99t file a route over an
inoperative VOR), and your VOR recei= vers must be=20 operational.  Of
course, you wouldn=E2=80=99t file GPS-Direct over=20= routes that=20 require RNAV
equipment (long distances in areas of sparse navaids), unle= ss=20 you have
RNAV equipment.  While this is commonly done, ask yourself= =20 what you=E2=80=99d
do if you had a RAIM failure on that segment.

= So, how=20 about your non-certified GPS?  If it has the functional
requirement= s of=20 the certified equipment, you should (I say) be able to
use it.  If=20 questioned, the burden of proof is on you that you have met
the=20 =E2=80=9Cnavigational equipment=E2=80=9D requirement of 91.205.  The FA= A could use
FAA=20 policy or applicable court decisions to decide otherwise, but here
thing= s=20 are grey.  At least you should ensure that your unit does the
integ= rity=20 monitoring that is at the heart of the TSO 129c requirements
and=20 limitations.  Then, you should use it as supplemental to your
prima= ry=20 system in the sense I just described.

If you believe your unit meets=20 these standards, is it ok to do GPS (and
overlay) approaches with it?&nb= sp;=20 If it contains the latest Nav data base
and it does the RAIM check=20 internally before you execute it, I say yes.
  The only difference=20 between enroute/terminal and approach phases is
the more stringent RAIM=20 requirement or the latter.

But the world of aviation has evolved, and= now=20 there are receivers
certified under TSO 146, which requires using the WA= AS=20 system.  If you
never wanted to do NDB, VOR, or ILS approaches, you= =20 could fly with this
GPS and a COM transceiver for all your flying, and s= ave=20 the money
needed for a DME, ADF, VOR, and LOC/GS receivers.  This T= SO=20 has tougher
requirements on position accuracy that can only be met by ad= ding=20 WAAS
error correction to your raw GPS position solutions.

Ground=20 stations around the U.S. receive raw GPS position solutions and
send the= ir=20 3D position error (they know where they really are) to
geosynchronous=20 satellites in the east and west.  Your WAAS enabled GPS
receives th= e=20 errors from those satellites and, by interpolation using
errors at groun= d=20 stations near you, adds a 3D correction.  The
WAAS-corrected soluti= on=20 is claimed to be accurate to a meter horizontal
and two meters vertical=20 (best case, I suspect).

The raw GPS solutions have an accuracy affect= ed=20 by the dilution of
precision (DOP), which comes from poor geometry (all=20= the=20 satellites
lumped close together gives a lousy solution).  As in an= y=20 triangulation
scheme, horizontal position is best measured if stations a= re=20 on both
sides of you (on the horizon left and right).  Since vertic= al=20 position
cannot be determined by satellites above and below you (the ear= th=20 is in
the way) your raw vertical position is not nearly as accurate as t= he=20
horizontal.  WAAS corrections largely fix that, so WAAS is critical= to=20
vertical operations, such as using GPS altitude for terrain avoidance=20
(TAWS systems) or doing GPS vertical approaches.  There are other l= arge=20
errors due to the slowing down of the GPS signal through the ionosphere=20
and atmosphere (light slows down a factor of about 9 in water), and=20
these too are corrected in real time since the ground stations=20
experience the same extra delays.

The Chelton Flight Systems are=20 certified under TSO 146, so they can be
used for primary navigaton. = ; So=20 if you purchase the experimental
Chelton system, can it be used for prim= ary=20 navigation? Since the FAA
also imposes integrity monitoring on 146 units= , it=20 must give integrity
warnings as specified by that TSO.  These inclu= de=20 measuring the
horizontal and vertical protection limits (HPL, VPL), whic= h=20 you will
find on the satellite page of the Garmin 480, the only other GP= S=20
certified under TSO 146.  The certified Cheton gives the required=20
integrity warnings through its Free Flight GPS engine and software, so=20
if your experimental Chelton uses that GPS engine (this is an option on=20
their Pro system) those warnings are given and (I believe) this=20
satisfies the FAA intent.

But the Chelton is currently certified=20= for=20 LNAV operations only, so
LNAV/VNAV and LPV approaches are verboten. = ;=20 Why?  If you are going to
track a vertical GPS course to LPV minimu= ms,=20 for example, an FAA
requirement in TSO 146 is to determine your position= 5=20 times per
second, not once as in all TSO 129 receivers and the=20 Chelton.  But
there is more.

The LNAV/VNAV and LPV approache= s=20 are called Approaches with Precision
Vertical (APV).  This means th= at,=20 in software, the full scale CDI
deflection is reduced as you go down the= =20 glideslope much as both ILS
localizer and glideslope courses reduce the=20= full=20 scale deflection as
you proceed to the runway.  The increased=20 sensitivity keeps you in a
smaller and smaller box, and you must abort i= f=20 you can=E2=80=99t keep the
needles off the pegs.

So here is anoth= er set of=20 requirements on refresh times and CDI
sensitivity.  By the way, the= re=20 is also an increased sensitivity
horizontally for LPV approaches, but no= t=20 for LNAV/VNAV, hence the
former have the lowest minimums and visibilitie= s=20 (generally).  At the
moment, the only GPS available, certified or n= ot,=20 that can meet these
requirements is the Garmin 480, so at the moment it=20= is a=20 moot point and
the real issue today is whether your WAAS GPS can be used= for=20 primary
IFR navigation.

The requirements extracted here from TSO=20= 129c=20 or 146 are by no means a
complete set, and it=E2=80=99s not clear whethe= r you need=20 to meet others not
listed.  There are requirements on environmental= ,=20 software, data, and
manuals for example, but I believe as for gyros, the= =20 main issues are
functionality (which includes fault detection).  As= the=20 pilot and
manufacturer of your aircraft however, the burden of proof is=20= on=20 you to
determine if you meet the 91.205 requirements for IFR=20 flight.

Finally, only you can decide what equipment is sufficient for= =20 your type
of flying.  Redundancy is important, and everyone will ha= ve a=20 different
comfort level with various backup options.  But I hope th= is=20 gives more
insight into using one of the many new GPS systems available=20= to=20 the
experimental

Keith Thomassen
 -------------------------------1131815330--