School of Engineering and Design
Loss of Control of Light Aircraft:
Balancing Cost and Safety in Flight Test
Mike Bromfield
Guy Gratton
SETP/SFTE 4th European Flight Test Safety Workshop
London 28~29, September 2010
1M
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School of Engineering and Design
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School of Engineering and Design
What’s the question?
•
GASCo 28 year review of GA fatal accidents
–
–
•
Why type variations
–
–
•
35-50% stall/spin
Significant type variations
C150 rate >> C152 rate (~17:1)
PA28 “Hershey Bar” wing ~population mean, tapered wing no
fatalities
Understand the reasons
–
–
For flying training
For design
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3G
School of Engineering and Design
Spot the difference…?
0.71 fatals/ 100,000 hrs
Cessna 150L
Cessna 152
0.04 fatals/ 100,000 hrs
4M
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10 events:
C150/C152 stall/spin fatalities
Events
Aircraft: Cessna 150 L/M
Aircraft: Cessna 152
Enviroment: Wind 30 kts+
Pilot: 2 POB
Pilot: Instructor
Task: Baulked Ldg
0
2
4
6
8
10
5M
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J31-Calibration
Methods & Equipment
Flight Test basics
Go-Pro Cockpit
mounted
camera
Appareo
GAU1000A
Flight Data
Recorder
Garmin 296
6M
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Flight Test Programme Build-up
•8 aircraft
•17 test sorties + 3 checkouts
+ 1 decline
•25hrs 35mins flight test
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7M
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Flight Test using Rental Aircraft
• Aircraft Variables (ageing?)
– maintenance, performance, W&CG
• Organisation
– Different priorities
• Flight test .v. Flight School
– Aft CG stalling at 3000ft anybody?
• Local environment
– Area & procedures, controlled airspace, ATC, Wx
8G
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School of Engineering and Design
Stick Force to Change Airspeed
Cessna 150L,M & 152 with Flaps a) UP b) DOWN (L30)
BTP/Sortie: 2008-06-02/03/04
A/C= Cessna F150L,F150M,C152
CG = Mid-CG
Vtrim = 84~88 KCAS
Cessna
F150M G-BCUH
05/03/10
Wt.= 1599 lbs
35.03" AoD (25.87%MAC/58.76%
d -CG)
69 KCAS (81 MIAS)
ortie: 2008-06-10
Cessna F152 G -BFLU
12/12/09
Wt.= 1655 lbs
33.8" AoD (23.78%MAC/50.71%
d -CG)
69 KCAS
Desirable Pull Force to Stall (PFtS – 10 lbf/4.4475daN)
F150L G-GBLR CR
F150M G-BCRT CR
C152 G-BOFL CR
Stall Boundary
Pull Force to Stall Boundary
50
Flaps UP
60
70
80
90
100
110
120
BTP/Sortie: 2008-06-02/03/04
A/C= Cessna F150L,F150M,C152
CG = Mid-CG
Vtrim = 66~68 KCAS
Polynomial Curve Fit for Apparent LSS - Landing (30)
7.00
6.00
KCAS >>>
HQR Climb & PointSpeed
Track
5.00
Desirable Pull Force to Stall (PFtS – 10 lbf/4.4475daN)
4.00
Start Climb
9
6
Desirable: +/- 2 MIAS/KIAS
Adequate: +/-5 MIAS/KIAS
3
G-BCUH F150M
0
G-BFLU F152
Stick Force Pull (daN) >>>
Stick Force Pull (daN) >>>
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
-1.00 40
-2.00
-3.00
-4.00
-5.00
-6.00
-7.00
ortie: 2008-06-12
Polynomial Curve Fit for Apparent LSS - Cruise
F150L L30
F150M L30
C152 L30
Stall Boundary
Pull Force to Stall Boundary
3.00
2.00
1.00
0.00
-1.00 40
50
60
70
80
90
-3.00
Flaps DOWN
-4.00
-6.00
Mid Climb
110
-2.00
-5.00
End Climb
100
-7.00
Speed KCAS >>>
9M
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Climbing Flight: Cessna 150M
Radio Calls >> Increased Workload??
10M
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Flight Test Results
• Variability between aircraft, C150 consistently lower pitch forces
– Mean gradient factors ~2-3
– C150 sometimes neutral (e.g. L40)
• Stick force dependent on:– (1) Flaps, (2) Power, (3) Trim, (4) Weight, (5) CG
• Low stick force >> poor airspeed management
• Stall warning
– C150 non-compliant with (current) part 23 in certain configs.
– Simultaneous stall warning + aerodynamic stall
11M
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Simulation Experiments
- Scenario-based Testing
Simulator
• PC7 Fixed-base research simulator
–
–
Controllable force feedback
150 x 40 deg. Visuals
Scenarios
• 20 pilots x 5 scenarios x 3 stick force gradients
–
Circuits, EFATO, Climb-out, Go-around, Base to Finals Turn
Data /Analysis
–
–
Workload (Heart Rate, NASA TLX)
Flight dynamics + RT/intercom
12M
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Typical simulator test results:
margin of safety & effect of stick forces
13M
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Example: Pilot 24
Go-around, Full Pwr / Full Flap
Non-dimensionalised AoA .v. Elevator
Alpha
Pilot 24 (high hrs):
• ATPL
• 12,000+ hrs PIC
• Age 60~64
• Avge 350+ hrs per yr
Key:
Stick Force Gradients
High
Medium
Low
Pilot 23 (medium hrs):
• PPL (no IMC)
• 1200+ hrs PIC
• Age 65~69
• Avge 33+ hrs per yr
Elevator
14M
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School of Engineering and Design
Conclusions




Type training - C150 and C152 are different
Design factors - Certification standards are too subjective,
consider use of Human Factors tools
Aircraft design, loading & configuration influence airspeed
management & stall avoidance via pilot cues
Low stick force gradients can result in:–
Poor airspeed management cues & stall avoidance cues
–
More mentally demanding tasks
–
Increasing workload
–
Decreasing safety margins
………which all makes loss of control due
to distraction or pilot inattention more likely
15
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Lessons Learned
• Independence
– Manage FTI, check maintenance
– Always check W&CG reports
• Workup
– Essential but spread across sites and aircraft
– Use learning curve
• Efficiency
– Critical test points
– Concentrate flying periods
• But always review data between sorties
• Best practice
– Qualified pilot opinion
– Redundancy in data collection
16G
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Any Questions?
Acknowledgements: Dr Mark Young
 Thomas Gerald Gray Charitable
Trust
 GASCo, UK-CAA
 Cranfield & Sheffield Universities
17M/G
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School of Engineering and Design
Type of Accident (UK) - 1980 to 2006 (GASCo)
Medical/Suicide
3%
Low Approach
4%
Airframe Failure
4%
Collision with Grnd
Object
5%
Undetermined
5%
Loss of Control VMC
25%
Mid-air Collision
6%
Loss of Control IMC
8%
Forced Landing
12%
Fixed Wing <5,700kg
(non-microlight) fatal
accident causal factors:
1980 to 2006 (UK)
CFIT
12%
Low Flying/Aeros
16%
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School of Engineering and Design
BFSL Safety Model
Boundary
(Unsafe
Condition)
+
Actual
Condition
-
Environ.
Safety
Margin
(Safety Cues)
Planned
Margin
Tracking
+
Point
(Optimal)
-
Condition
Error
(Condition
Cues)
Pilot
Gust/Turbulence
+
Control
Inputs
Control
System
Control +
Outputs
Aircraft
Dynamics
Aircraft
Pilot
Actual
Condition
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School of Engineering and Design
Cessna 152
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School of Engineering and Design
HQR - Climb & Point Track C152, F150M
BTP/Sortie: 2008-06-12
A/C= Cessna
F150M G-BCUH
Date: 05/03/10
Gross Wt.= 1599 lbs
CG = 35.03" AoD (25.87%MAC/58.76%
CG/Mid -CG)
Vtrim = 69 KCAS (81 MIAS)
BTP/Sortie: 2008-06-10
A/C= Cessna F152 G -BFLU
Date: 12/12/09
Gross Wt.= 1655 lbs
CG = 33.8" AoD (23.78%MAC/50.71%
CG/Mid -CG)
Vtrim = 69 KCAS
HQR Climb & Point Track
Start Climb
9
6
Desirable: +/- 2 MIAS/KIAS
Adequate: +/-5 MIAS/KIAS
3
G-BCUH F150M
0
End Climb
G-BFLU F152
Mid Climb
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School of Engineering and Design
Sim. Experiment 3:
Workload Results
8.0
30
Mental Demand - All Stick Force Gradients
7.0
Total Workload - All Stick Force Gradients
25
6.0
5.0
4.0
20
3.0
Mental Demand - High
2.0
15
Mental Demand - Medium
Mental Demand - Low
1.0
0.0
10
***Practice Circuit***
BRS Rwy 27
Total Workload - High
Circuit
BRS Rwy 27
Total Workload - Medium
5
Approach & FULL Flap
Landing @65 kts, Rwy 27
2nm
700' AGL
(with Go-around)
Base to Finals Turn
w/landing
BRS Rwy 27 R/H
Mid-base
750' AGL
Total Workoad - Low
8.0
0
Physical Demand - All Stick Force Gradient
7.0
***Practice Circuit***
BRS Rwy 27
Circuit
BRS Rwy 27
Approach & FULL Flap
Landing @65 kts, Rwy 27
2nm
700' AGL
(with Go-around)
Base to Finals Turn
w/landing
BRS Rwy 27 R/H
Mid-base
750' AGL
6.0
5.0
4.0
‘High’ Stick Force :- Lower Mental Workload
- Higher Physical Workload
3.0
Physical Demand - High
2.0
Physical Demand - Medium
Physical Demand - Low
1.0
0.0
***Practice Circuit***
BRS Rwy 27
Circuit
BRS Rwy 27
Approach & FULL Flap
Landing @65 kts, Rwy 27
2nm
700' AGL
(with Go-around)
22
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Base to Finals Turn
w/landing
BRS Rwy 27 R/H
Mid-base
750' AGL
School of Engineering and Design
Example: Pilot 24
Climb-out, Full Pwr / Zero Flap
Non-dimensionalised AoA .v. elevator
Pilot 24 (high hrs):
• ATPL
• 12,000+ hrs PIC
• Age 60~64
• Avge 350+ hrs per yr
Key:
Stick Force Gradients
High
Medium
Low
Pilot 23 (medium hrs):
• PPL (no IMC)
• 1200+ hrs PIC
• Age 65~69
• Avge 33+ hrs per yr
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School of Engineering and Design
Example: Handling assessment in climb-out
Workload
Speed
Point
Tracking
(Maintain)
1.3 VStall
1.2 VStall
1.1 VStall
VStall
13 (Sat.)
‘Top-down’
46 (Unsat.)
79 (Unaccept.)
10+ Control lost
@crossover switch from
‘top-down’ (point
tracking) to ‘bottom-up’
(boundary avoidance)
‘Bottom-up’
Boundary
Avoidance
(Avoid)
Time
Cooper-Harper for boundary avoidance – can be automated
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School of Engineering and Design
Conclusions – Causes of LoC
•
Stall Boundary crossing (not point tracking)
–
•
Type training
–
•
A C150 is not a C152
Design factors
–
–
•
Handling characteristics & workload
Certification standards are too subjective
Consider Human Factors tools
Further work needed
–
–
Historical certification standards for stalling
Apparent LSS results and models (FCMC in longstab calcs)
25M
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