NATOPS, Reports, Issues and how they relate to the Marana Accident
the Red Ribbon Panel, Jan 2002)
The following are the results of our studies to review and determine if there
direct or indirect connection between:
(a) Deleted/deferred flight testing (as reported by last years GAO and DOD/IG
(b) Limits for Pilots in the NATOPS Flight Manual,
(c) Performance Test Data and JORD requirements,
(d) Potential impact/errors in JAGMAN investigations and conclusions.
1. Background Information
a. NATOPS Limitations directly related to the Marana Accident:
Normal Load Factor for VTOL/Conversion Mode are -0.5 G to 2.0 G
--- with Max Angle of Bank of 60 Degrees.
(" " "
" " "
" Airplane Mode"
" -1.0 G to 3.5 G --- "
" " "
" " " 60-75
Note: These limits as related to VTOL/Conversion mode are not supported
by actual flight testing.
b. Warning concerning Settling with Power in NATOPS
"Avoid descent rates of 800 ft/min or greater at airspeeds less
than 40 KCIAS."
There have been several questions asked as to where/how this was decided to
be included in the NATOPS Flight Manual. We have found no information based
on actual V-22 flight testing for determination of these limits, which
are related to VRS. There has been no explanation as to how these Limits were
determined as they relate specifically to the V-22 Tiltrotor.
The only indication found, lacking any evidence of V-22 flight testing prior
to the Marana accident, was contained in a Navy Helicopter Training
manual which applied to the much earlier and smaller TH-57 Trainer
"Vortex Ring State - The uncontrolled rate of descent caused by the
helicopter rotor encountering disturbed air as it settles into its own downwash,
also known as power settling. This condition may occur in powered descending
flight at low airspeeds while out of ground effect, when rate of descent
approaches or equals the induced flow rate. At 300 - 600 ft/min descent,
vortex ring state may begin and will not clear until exceeding 1500-3000
ft/min. Glide slope of 70 degrees (nearly vertical) seems to
increase the possibility of settling. When these conditions are met, the rotor
pumps air into a large bubble underneath it, which then bursts, disturbing air
flow and blade thrust. Because approach angles less than 50 degrees and
airspeeds of 15-30 kts allow enough new air to enter the rotor system, the TH-57
is limited to descent rates less than 800 ft/min, with airspeeds greater
than 40 KIAS, and approach angles less than 45 degrees. "
If in fact, this or similar helicopter flight manual were the source for the
V-22 NATOPS Manual Warning - as opposed to actual flight test verification by
the Contractor/Navair/NASA - it would be a serious oversight by all
The application of past experience in smaller Helicopters to derive Limits for
an unknown/untested laterally displaced - side by side - rotor aerodynamic
system, would be a gross error.
Note: It is a matter of interest that one month AFTER the mishap,
Navair issued Urgent Change No. 1 to NATOPS, adding a description of high rates
of descent in VTOL Mode and the procedures to recover from this
It is also of interest throughout the Jagman report, that flight in the V-22 is
only discussed in a two-dimensional consideration. There is no discussion
related to the fact that the V-22 must and does operate in a three-dimensional
airspace. Discusion of lateral and yaw controls and their impact on the above is
not presented, nor are any of the other flight situations involving Multi-Axis
controls presented or discussed.
As will be shown later, the only guidance found was the NATOP Limits of 2.0G and
60 Degree Angle of Bank in VTOL/Conversion mode. The reason for a Prohibition of
rapid multi-axis controls is not explained so as to alert the pilots of how this
impacts on the foregoing.
It appears through what little information/research is available in the public
domain, that neither Navair nor NASA had any idea or direct knowledge,
through V-22 Flight testing prior to Marana, about the real flight
"boundaries", other flight limits or any critical effects of
maneuvering. They do in fact appear to be arbitrary and based on
earlier helicopter limitations.
Despite the foregoing, the above limits/warnings in the V-22 NATOPS appear to
have been incorrectly applied in the JAGMAN and Safety Investigations in
determining if pilots had exceeded them in violation of the NATOPS.
c. Navair/Bell/Boeing Flight Test Performance Data Chart.
This chart (attached) provides results of actual flight testing,
presented to the Blue Ribbon Panel, which should have been used as the
factual/experimental basis to derive the proper limits for NATOPS Flight Manual
The average Maximum Load Factor (Nz = "G") displayed on this chart
show a Maximum average of Nz = 1.15 to 1.20 'G"s for Hover/Conversion
Note: This indicates level flight demonstrated Load Factors. No
information was given as to the Load Factor Capability
in descending flight, which would have been more critical in the
conditions involved in the Marana accident case.
This minimal Load Factor in turn projects a Maximum Angle of Bank of
about 25-30 Degrees.
Note: This estimate is also based on the level flight test only. It might
actually be less in descent if the Rotors are Stall Limited. In descent the
pilot would have more collective control available to use, which would make it
easier to readily exceeded these minimal levels, before power (torque) limits
It should also be noted that the performance envelope "goals" - as
shown by the dashed lines for each nacelle angle test segment on the
chart - indicate that the V-22 Goal for Load Factor in the VTOL/CONV mode
was approximately Nz= 1.75 G's, which was significantly higher than
actual testing demonstrated.
d. JORD Requirement Charts, dated 15 Feb 2001
(included in Appendix to Final Blue Ribbon Panel Report).
The established JORD Requirement Number 028 requires:
Instantaneous G Loading of +3.0 to -0.5 instantaneous G's in Helicopter
" " "
" " "
" +3.5 to -1.0 "
" " "
" in the Airplane Mode.
It is obvious from the performance testing that the V-22 cannot
generate +3.0 G's in the Helicopter Mode.
It is therefore interesting to note that the Current Status of this
requirement is Graded in Green indicating "Full Capacity Exists
or Threshold Met"
The inference of this claim also suggests the conclusion that a bank of 65-70
Degrees, which has also not been (and could not be) demonstrated.
No data to support this gross conclusion has been found in any test reports.
The various items for Limitations required of pilots as noted in the
NATOPS are not supported by either the Flight Test Performance Charts, nor the
grading shown in the JORD Requirements which has been graded as being
We now have the following variations in "G Loadings" in
Helo/Conversion mode ranging from:
+1.2 G in actual Flight Testing
+2.0 G claimed in NATOPS
+1.75 G goal of Flight Test
+3.0 G claimed as completed in JORD Requirement Status Report
It is obvious that the unexplained variations of information in this area of
V-22 Performance capabilities and limits,
are completely impossible to reconcile. (Person or persons responsible
should be interviewed/investigated as necessary)
e. Pilots Decisions
Assuming that most Line Pilots are not aware of anything except the NATOPS
limits, which are considered by pilots as their flight "Bible"
(i.e., not open for argument), we can conclude that a pilots primary basis for
decisions are dependent on published limitations in the NATOPS Manual.
Pilots would normally be correct in assuming (but incorrect in reality)
that they could safely make 60 Degree banks at 2.0G during flight in
Helo/Conversion Mode; which in reality could lead them immediately into
an asymmetrical STALL.
It is inconceivable, given the foregoing that a pilot following NATOPS
could be found the Cause of a mishap such as the Marana Accident.
2. V-22 Test Program problems directly related to Marana Accident:
As related to several above reports, the testing in the 0-60 Knot airspeed
ranges, which was required to provide accurate data for determining limits
for NATOPS, was deferred/deleted/ignored, before the aircraft was
released to line Pilots ( who were NOT Certified Flight Test Pilots
Load Factors for VTOL/CONV Modes, as well as warnings referenced to VRS,
were apparently and wrongly adapted from other standard Helicopter NATOPS
No evidence has been seen which would allow any other conclusion to be made.
3. Jagman Investigation of Marana Accident:
A review of the Jagman investigation indicate that several items of
interest were either ignored, missed or left out which directly involved
the findings and conclusions. Many of these would have been changed if they had
been studied, evaluated, and included in the investigation. Absent the
information above, it becomes apparent that insufficient data and knowledge was
available to the investigators to permit more accurate/complete conclusions.
Extracts from Jagman Report
a. "The Mishap Aircraft's flight profile in the terminal area (high
descent rate/low airspeed) most likely resulted in the aircraft
experiencing a Vortex Ring State (Power Settling) and /or blade stall condition,
which resulted in departure from controlled flight and the subsequent
b. The report also stated that this condition is "more extreme
than the results experienced in most rotorcraft to date."
The Deputy Commandant for Aviation did NOT concur with this statement.
Note: In the history of helicopter flight operations, we have never found
a case where a Helicopter did a snap-roll onto its back and crash into the
ground - because it got into a Vortex Ring State (VRS). An encounter of
helicopters of a VRS condition is a very rare condition.
When a former FAA Flight Test Pilot with some 40+ years of flying helicopters,
was asked what comments he had to offer about the recent flurry of attention by
Navair and NASA of the "VRS" problem, he seemed surprised - and
asked "What is VRS?"
Given that this is a well known fact to all helicopter pilots and
aero-engineers; someone should determine why the General non-concurred, and
also why others - including Contractors/NAvair?USMC/NASA - have repeated similar
c. "This unfortunate mishap appears not to be the result of any
design, material, or maintenance factor specific to tiltrotors"
This conclusion appears to be inconclusive and misleading and has been
repeated for the past few years.
It asserts that the V-22 Tiltrotor aircraft "appears" not to
have any design problems.
Efforts by the Red Ribbon Panel over the past year has shown that this is not
It has a very basic and major design flaw in its rotor design and
This has been demonstrated by: default of testing and performance, numerous
limitations and warnings related to control uses by the pilots, and more written
emergency procedures and warnings/cautions in the V-22 NATOPS flight manual than
any other military/civil aircraft known in current service.
Note: A thorough human factors engineering analysis of the amount of
material to be absorbed by the pilots would be of great value to explain the
level of difficulty required to safely operate the V-22 in combat maneuvering
conditions -- which are prohibited (even after some 10+ years of flight
operations). As will be seen later, the Marana accident aircraft were, by any
evaluation, one of the first actual examples of routine combat maneuvering in
formation at low airspeeds altitudes. They operated in an envelope area which
had NOT been tested by either the Contractor or Navair.
The Major Design Flaw is directly related to the laterally displaced
Rotor/blade design, which produces little or no combat maneuverability.
This was reported by the Red Ribbon Panel on 14 May, 2001.
The only test data known are the Six flight test Data Points shown on the
Bell-Boeing/Navair Performance Flight Test Chart, which indicates a maximum
limit load capability of Nz= 1.2 "G"s. This provides a
very small 2/10 of a G margin for any maneuverability or agility, which when
coupled with the Lateral (side by side) Rotor design creates a significant
and deadly design fault.
This has been known or should have been known for many years. This
finding is supported by (1) lack of flight test, and (2) the use of numerous
warnings or cautions in the V-22 NATOPS Manual directly related to the lack of
1. Combat Maneuvering is prohibited.
2. Autorotations are Prohibited
3. Abrupt multi-axis control inputs are Prohibited
As reported before, the V-22 is not - and cannot - be used in any terminal
mission Combat area, susceptible to enemy fire.
DOD studies of rotary-wing losses in Vietnam and subsequent areas of
hostility , have shown that 91% of losses were in the Terminal Mission
Area. (As one of our pilots have said - it is a "sitting
duck" in any Combat Situation! Another combat helicopter pilot offers that
"a Combat V-22 is an oxymoron.")
The "cover phrase" added to the Gen McCorkle comment in item c.
above is: "--factor specific to tiltrotors" .
This is an intriguing phrase.
The design flaw in question is ONLY a factor specifically applicable
to the V-22 tiltrotor!
The Major V-22 design flaw is not associated nor applicable to ANY
The use of laterally (side by side) displaced rotors creates a complex
problem - which has been subject to little or no testing in low
airspeed/low altitude ranges.
The impact of winds, gusts, turbulence and control inputs have not been subject
to any specific testing, nor any Technical Reports from either NASA or NavAir.
Note: A search of both AHS (American Helicopter Society) and NASA
Technical Report Databases reveals not a
Single Report Addressing VRS or Maneuvering Issues with the V-22 prior to 2001!
The coupling or addition of laterally displaced propulsion, with twin
rotors which have the lowest limit load factors for hover than any known
Military Combat Capable Rotorcraft; results in what IS a Major Design Flaw,
which SPECIFICALLY applies to only this tiltrotor - the V-22. It is a
Flaw in that it has not been tested nor demonstrated that it can perform safely
in its intended role as a combat capable aircraft.
The Marana accident would appear to be first proof of this. Given the test
results, it is believed that this aircraft would not be certifiable by the FAA
for civil use.
It is interesting that the Memorandum of Understanding between Navair and the
FAA, which provided that the FAA flight test pilots would be directly involved
in the testing of the V-22 was later waived by the Navy. Given the normal
thoroughness of FAA Flight Testing Standards, it may be of interest to
investigate why/how this occurred.
Roll Damping and Roll Inertia
Unlike a helicopter where the tail rotor act as a large Roll Damper, and the
central location of the rotor precludes any real problems with Roll Inertia;
The V-22 has little or no Roll Damping, and a very large Roll Inertia.
Locating the engines and transmissions and rotors at the end of the wings (even
though the wings are fairly short) makes the roll inertia huge compared to a
helicopter and large even by commercial airplane standards.
This large inertia will mean that when a significant roll rate is
established, it will be very hard to arrest by normal control inputs
Arresting a significant roll rate caused by control inputs (maneuvering
bank or turn) or a powerful external disturbance (such as flying into the wake
of another aircraft) may have:
1. been beyond the pilots normal control limits,
2. beyond the power (rotor torque) limits,
3. within the control/power limits but one of the rotors stalled because of
the low stall margins on these rotors and large differential collective
pitch applied through the control inputs, or
4. the control response rate was just too low to be effective (aerodynamic
The application of differential collective in a banking situation probably
helped to stall one of the rotors, promoting an even more powerful roll in the
With the high roll inertia combined with the low roll damping, it could well be
that this is one reason that maneuvering limits were placed on this aircraft
when in helicopter mode. We suspect that this was determined early on from
flight simulation work, and written into the NATOPS.
If this is correct, then it may become another example of where the JORD called
for a certain level of maneuvering capability and the contractors went ahead
anyway hoping that they could get around this deficiency somehow, most likely by
changing the JORD to fit the capabilities of the aircraft.
There is NO fix or design change which will cure this Design Fault -- without
a complete aircraft redesign.
d. Annex A of the Jagman Report Synopsis.
It is of passing interest to note that this annex discusses VRS in BOLD
face print, while 'stall' is in normal print and not capitalized.
The discussion of Blade Stall correctly relates Angle of Attack (not mentioned
in VRS discussion), to blade stall -- and to stall region on "one
prop-rotor while decreasing the stall region on the other."
4. Asymmetric Stall Considerations
The probability of Asymmetrical Stall was apparently not considered as a
serious factor in the investigation, or it might have been noticed that the
maneuvering of Mishap aircraft from formation high left to formation high right
followed by realignment with lead aircraft, would be a perfect setup
for asymmetric stall on the right rotor. The rotor at this time enters an unusually
high Blade Loading and low Stall Margin.
It should be noted that none of the published reports or tests include any
multi-axis control testing. All of the past TR-64 tests for examining VRS
conditions have been done only with fore and aft cyclic inputs to help
The absence of differential lateral cyclic or rudder inputs may result in
the realities that the new boundaries/limits MAY NOT be adequate or SAFE if
and when any lateral or multi-axis inputs are required!
Given the higher density and temperatures involved at Marana, the Nz (G's)
available for maneuver would have been reduced enough (G = 1.15-1.20)
to cause any significant banking in formation maneuvers -- added with yaw
pedal activation -- to exceed the Stall Margins during the interval between
the approximate times of 19:57:30 (aircraft in conversion mode) and 19:57:57.
There is no indication in the Jagman Report that any consideration of the
relationships noted in the foregoing information and data was given.
There was also no information found in the Jagman Report on pages 53-54, where
some Eight or so NATOPS provisions were discussed; which might have drawn
attention to the specific limits to the pilot in regard to the
"incorrect" NATOPS 'G' capability, nor the incorrect banking
capability/limits for the pilots.
It can reasonably be accepted that the average line pilot does keep in mind
the normal/standard limits - as opposed the aircraft special limits.
The fact that NATOPS could lead a pilot to believe that under the conditions for
hover/conversion mode (2.0 G and 60 Degree Bank) when such capability did not
exist, could easily have been the primary factor in this accident.
The apparent rush or jump to discuss VRS as opposed to Asymmetric Stall
apparently caused the JAG to assign fault to the pilot. There was no indication
that consideration was given to the assumption that the pilot might have been
following the correct or specific procedures following NATOPS stated
rules/limits. The selection of criteria for avoiding a little known
phenomenon of "VRS" as opposed to clearly stated control limits in
NATOPS would have been an incorrect judgment by the investigators. This would be
a tragedy and should be reviewed and corrected as necessary.
The Jagman Report apparently does not provide continuous readings of the CSMU
(Crash Survivable Memory Unit) for the last fifty seconds of flight between
the initiation of Conversion for the 2nd Aircraft; through the Crossover and
bankings required during conversion to change formation sides, and the need to
to get realigned with lead when he is in High-right position.
The maneuvering necessary to follow lead into a left hand formation turn,
while initiating conversion and maneuvering from left high to right high was not
discussed in the Report.
A complete time line discussion, including not only the following, but
one which should include other registered CSMU parameters, might have provided
Angle of bank information which would allow a second by second reconstruction to
perhaps validate a rotor stall, instead of reaching a premature conclusion
supporting the 'VRS' theory. Any attempt
by the pilot to maneuver under the Standard NATOPS limits for helicopters of 2.0
"G"s and 60 Degree Angle of Bank would have produced an immediate
right rotor stall.
(Note: Airspeed has been converted to give a better view of ROD/Airspeed
Nacelle(Deg) AGL(ft) ROD(fpm) Airspeed(fpm) AS/ROD
12.59 began crossover, unknown
on right side
slowed, slight balloon
bank, 3 O'clock High
Multiple axis controls were clearly involved in the maneuvering control actions
required in formation flying.
WHY WERE MULTI-AXIS CONTROL INPUTS PROHIBITED IN THE NATOPS?
This should have raised a Red Flag in the JAG Investigation, that there
was in fact something already known by Navair/Contractors/NASA about the V-22
maneuvering control problems.
What was known that established this concern and prohibition - other than lack
or cancellation of flight test -- and why wasn't it addressed properly in the
NATOPS to preclude inadvertent accidents?
At (:13 sec), a/c began conversion from Airplane mode to Helicopter Mode, with a
rapid decrease in airspeed from 18840 fpm to 11140 fpm at (:14sec) (if CSMU
Between (:14sec) and (:35sec) the a/c began crossover maneuver, with unknown
angle of bank, while continuing conversion from 0 Degree to 51 Degree nacelle
angle, and very rapid descent required to follow lead in his descent from the IP
3 Seconds later CSMU indicated at (:38 sec) that the aircraft was somewhere on
"right side". Jagman reports nacelle at 73 Degrees, but provides
no data re A/S, ROD, bank angle, or AGL, for this critical time period.
At (:44 sec), conversion was almost finished, with 90 Degree Nacelle, and the
a/c slowed and made a "slight" balloon event.
The airspeed was still slowing, and the ROD had slowed significantly from 3945
to 150 fpm.
Given that between (:35 sec) and (:44sec) the a/c was in crossover
maneuvering; followed by a slight balloon and needing formation correction
to left a few seconds later ( :50 sec), the pilot made a left bank (of
unknown amount) with an A/S to ROD ratio of about 6.53/1.
Given the several time gaps - some significant-in the Jagman Rpt, a
definitive time when the aircraft may have entered a maneuvering stall or
encountered VRS is hard to establish. The maneuvering time zone between :35 and
does show that a definitive Left Bank was made at :50Sec.
It would appear that in making a Left bank, the a/c exceeded the
aircraft's actual "G" and Banking limits
(probably with about Nz=0.2 G reserve with less than 5-10 Degree bank
capability), which probably stalled out the Right rotor!
(Note: The only real guidance available to the average pilots was that NATOPS
limits were 2.0G and 60 Degree Bank. The actual Bell/Boeing/Navair Flight
Test Performance Chart indicates that Max Maneuver Lift reserve was about
0.2 G!! in the 0-60Knot range!!!!.) This indicates that neither the Lead
aircraft nor the Accident Aircraft had sufficient maneuver margin to proceed in
flight conditions (which would not have affected any other Military Helicopter).
Since the NATOPS manual appears to have included incorrect information that
had not been validated by any actual flight testing, any pilot left in the
above situation-regardless of training to the contrary -- may have had no
reason NOT to use standard banking techniques in formation maneuvering. His
ignorance of this situation might well have resulted in the unnecessary deaths
of all aboard the mishap aircraft.
IF the CSMU data which could fill in the missing time and Bank Angle
information was plotted, or if it is available in one of Jagman
Appendices, a complete review should be immediately accomplished!
VRS is an interesting subject, but the unknown and untested results of
Asymmetric Thrust and Lift parameters associated with a blade/rotor stall
limits, may well be far more important to Pilots, particularly in the lower
airspeed/altitude terminal mission areas which require a high degree of
maneuverability under pressure.
Taking into consideration:
1. the conflict of statements and documents related to the Flight Testing
results and the determination or signing off of incorrect G Limit factors both
in NATOPS and In JORD Briefing Charts,
2. the lack of availability to put correct data, limits and proper discussions
in the NATOPS Manual,
3. the lack of adequate discussion related to asymmetric configuration under
various situations involving both Stalls and VRS,
4. the lack of inclusion in the 'Findings of Fact' of any scenario formation
maneuvering and use of flight controls/timing which would have led to a more
probable conclusion of an Asymmetric Stall,
5. the unwarranted decision to place the onus on the pilot for not complying
with NATOPS, when NATOPS did not cover the relationships between Maneuvering
considerations necessary to fly in formation flight (and at the same time
avoiding the PROHIBITION against Combat maneuvering).
Recommendations for Investigation:
1. The basis for statements by any personnel offering as facts the
"sameness of the V-22 and helicopters" when such conclusions were
baseless, and can lead to carelessness and accidents.
2. The basis for the administrative or negotiated elimination/deferral/deletion
of tests which were required (by contract?) for use as a sound basis, for the
determination compilation of correct/validated FACTS for use in the NATOPS
3. The basis for consideration by Navair for certification of airworthiness
and/or clearance for Line Pilots prior to completion of flight testing and
acquisition of the data required to establish proper NATOPS instructions,
Warnings and Cautions.
4. The basis for decisions related to the assignment by Navair to the
Contractors for the primary responsibility for the Flight Test Program
requirements established under the ITT (Integrated Test Team) concept
5. Lacking adequate testing, the basis on which the Contractors and Navair used
to insert in NATOPS material which was in error, false, or misleading and which
would in turn lead otherwise qualified pilots into unfamiliar and dangerous
6. The apparent use of outside advisors/consultants/officers, not familiar with
the true performance and behavior of Asymmetric tilt rotor Propellers (as
opposed to conventional helicopter rotors), and the numerous situations waiting
for the uneducated pilot not familiar with the idiosyncrasies involved.
7. The degree of the management awareness of the decisions related to all of the
foregoing, and any obvious misrepresentations under contract related to all of
the above obvious discrepancies.
8. Given that the real primary cause was the failure in airworthiness of
the unique design of the asymmetric propeller system, which had not been fully
and properly tested and certified; consideration should be given to set aside
any assertion or conclusion that the pilot of the mishap aircraft be deleted
from all correspondence, reports and announcements related to this mishap.
9. Finally it is recommended that based on the above, that the conclusions
reached by the Jagman investigation should be set aside, until and unless more
testing of the aircraft related to both Asymmetric Stalls and VRS can conclude
that the aircraft is certifiably safe in the same degree as that required by the
FAA for transport aircraft.
Note: It appears that not a single person on the Blue Ribbon Panel had
any real experience in Rotorcraft aerodynamics, flight testing and operations;
which otherwise might have resulted in the discovery of most of the above
findings. All of the material above was available in the briefing materials
provided to them, and in the NATOPS Flight Manual. These were the same documents
used by the Red Ribbon Panel in our research and studies which produced most of
the foregoing materials and discussion.
The above information solidly indicates that the V-22 rotor system is in fact a
FLAWED Safety of Flight Design, which CANNOT be 'fixed " without a
complete aircraft re-design.
It should be terminated immediately , before more men are killed.
Harry P Dunn
Coordinator, Red Ribbon Panel