Helicopter precision approaches using GNSS

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Helicopter precision

approaches

using GNSS

Philip Church

25 April 2013

Presentation for IET EC3 Section

1

Helios is the leading management and technology

consultancy in air transport

We aim to be our customers’ first choice

Company overview

Performance

improvement

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improvement

RegulationRegulation

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EnvironmentEnvironment

Technology & innovationTechnology & innovation

Planning & procurementPlanning & procurement

TrainingTraining

Performance

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improvement

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Technology & innovationTechnology & innovation

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TrainingTraining

• leading consultancy specialising in air

transport, airports and in Air Traffic

Management

• Also working in space, rail, maritime,

telecoms and defence

• Established in 1996

• Joined Egis, an international

engineering and infrastructure group,

in January 2013

• Headquarters in Farnborough UK

• Turnover: ~£5M

• Over 70% of revenue from exports,

mainly within Europe

• Two Queen’s Awards for

Enterprise (2004, 2009)

Customer base

Services areas

Overview

2

Difficulties of the offshore environment

‘Existing’ approach procedures

‘Safety’ assessment of ‘existing’ procedures

Proposed mitigations

Future steps

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Difficulties of the

offshore environment

3

4

Operations

Helicopter precision approaches using GNSS 5

Helicopter routes in the North Sea


Platform locations in the North Sea

8

Flights during low cloud base

• Navigation based on Airborne Weather Radar Approach

(ARA)

• Defined in:

• TSO C63c - (Airborne Weather and Ground Mapping Pulsed

Radars)

• TSO C102 - (Airborne Radar Approach and Beacon Systems for

Helicopters)

9

Standard first established in 1959!!

The ARA

10

No vertical guidance / Low level turns

ARA guidance

11

+-- LUM +-- BRG

ON/OFF +-- CRTSDMAP MISD NAVD FND

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Existing regulatory

(equipment)

requirements

12

Equipment carried

13

Industry standards

• Standards checked in relation to weather radar:

• TSO C63c - (Airborne Weather and Ground Mapping Pulsed

Radars)

• TSO C102 - (Airborne Radar Approach and Beacon Systems for

Helicopters)

• AC 90-80B - (Approval of Offshore Standard Approach

Procedures, Airborne Radar Approaches, and Helicopter En

Route Descent Areas)

• RTCA DO-172 - (MOPS for Airborne Radar Approach and Beacon

Systems for Helicopters)

• RTCA DO-173 - (MOPS for Airborne Weather and Ground

Mapping Pulsed Radars)

• Standards checked in relation to radio altimeter:

• TSO C87 – (Airborne low range radio altimeter) 14

What do the standards describe?

• Maintenance requirements

• Performance requirements

• accuracy

• range

• azimuth

• target size

• Test procedures

• during maintenance

• during pre-flight checks

15

Point of interest

AC 90-80B

TSO C63c TSO C102

DO-172 TSO DO-173

Indicated range error:

• ± 0.2NM for displays of

5NM or less


• < 10% of actual target

distance, or

• 1NM, whichever greater


• < ± 600ft (2) for

distances of 5NM or less for

Phase I

• < ± 300ft (2) for Phase II

• < 5% of indicated range

for ranges > 5NM

16

RDR-1400 technical specifications

• Certification:

• Radar certified by FAA to:

° TSO C63b

° TSO C102

• Installation and maintenance manuals supplied in accordance

with TSO.

• Repairs are upon fault indication or pilot malfunction report.

• Reliability:

• False alarm rate is 5 indications per 120º scan i.e. 10-6.

• Accuracy with respect to range and azimuth meet and exceed

the +/- 2% requirement of TSO DO-172 and 173.

• Expected MTBF of 1600 hours in continuous use.

• Analyzed to have a probability of generating misleading data of

2.18 x 10-6.

17

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Safety concerns

18

Mandatory Occurrence Reports (MORs)

20

Event type Number of

occurrences

First report Latest report

Incorrect or unavailable wind data

provided

4 April 1976 November 2003

Incorrect QFE/QNH to a/c 6 December 1977 February 2001

Crashed in poor visibility 1 November 1981

Loss of separation between helicopters 1 November 2004

Descended below decision height 1 June 2003

NDB procedural problem 1 March 1983

Helicopter landed on wrong rig 11 July 1989 November 2004

Misidentified rig 2 May 1990 August 1994

NDB off on rig 1 March 1981

NDB interference 4 April 1986 June 1994

Loss of weather radar 1 February 1984

Erroneous ADF display 1 April 1996

Loss of displays 1 August 1999

Malfunction of altimeter 5 August 1985 March 2001

Helicopter Operations Monitoring Programme

(HOMP) events

• The two incidents recorded are:

• Helicopter climbing into cloud on approach

° Flight crew inadvertently climbed 50ft into cloud base

• Helicopter breaking vertical minima on approach

° Flight crew incorrectly flew approach at below minimum descent

height

21

Confidential Human Factors Incident Reporting

Programme (CHIRP) - Hazards

• Pilot descending below MDH

• Weather radar not calibrated

• Approach too close to rig (horizontal minima now

changed)

• Approach below deck height (vertical minima now

revised)

• Miscommunication between crew

• Weather radar not calibrated

• Crew breaking minima / ad quality of Met data

• Pilot descending below MDH

22

Risk matrix assessment

• EASA CS 25.1309 risk matrix

• EASA probability classification

23

Severity

CATASTROPHIC HAZARDOUS MAJOR MINOR

Fre

quency PROBABLE UNACCEPTABLE UNACCEPTABLE UNACCEPTABLE TOLERABLE

REMOTE UNACCEPTABLE UNACCEPTABLE TOLERABLE NEGLIGIBLE

EXTREMELY REMOTE UNACCEPTABLE TOLERABLE NEGLIGIBLE NEGLIGIBLE

EXTREMELY IMPROBABLE TOLERABLE NEGLIGIBLE NEGLIGIBLE NEGLIGIBLE

Frequency category Quantitative description

PROBABLE Failure condition frequency is more than 10-5 per aircraft flight hour

REMOTE Failure condition frequency is between 10-7 and 10-5 per aircraft flight hour

EXTREMELY REMOTE Failure condition frequency is between 10-9 and 10-7 per aircraft flight hour

EXTREMELY IMPROBABLE Failure condition frequency is less than 10-9 per aircraft flight hour

Offshore Weather Radar Approaches – Safety

assessment

24

Conflict Scenario

Severity

Probability

Result

1a. The flight crew approach the wrong installation and come into

conflict with another helicopter.

CATASTROPHIC

EXTREMELY

IMPROBABLE

TOLERABLE

1b. The flight crew land on the wrong installation and it is in an

unsafe condition.

CATASTROPHIC

EXTREMELY

REMOTE

UNACCEPTABLE

2a. The helicopter comes into conflict with the sea due to crew error.

CATASTROPHIC

< EXTREMELY

IMPROBABLE

NEGLIGIBLE

2b. The helicopter comes into conflict with the sea due to altimeter

failure

CATASTROPHIC

EXTREMELY

IMPROBABLE

TOLERABLE

3a. The helicopter comes into conflict with an obstacle due to flight

crew error.

CATASTROPHIC

EXTREMELY

IMPROBABLE

TOLERABLE

3b. The helicopter comes into conflict with an obstacle due to the

absence of the obstacle on the weather radar display.

CATASTROPHIC

EXTREMELY

IMPROBABLY

TOLERABLE

4a. The helicopter comes into conflict with the destination installation

due to flight crew error.

CATASTROPHIC

REMOTE

UNACCEPTABLE

4b. The helicopter comes into conflict with the destination installation

due to unannunciated weather radar malfunction.

CATASTROPHIC

EXTREMELY

REMOTE

UNACCEPTABLE

So something better is needed

• Manually interpreted

approach

• Reliance on the weather

radar for obstacle

clearance

• Helicopter operations can

be limited by lack of

navigation equipment

25

• GPS/SBAS can help, but limited use so far

• Increasingly dependent on GPS with gradual removal

of NDB’s from platforms

CAA requires action

• CAA Paper 2009/06 noted failings of current facilities

and improvements from GPS stating:

26

“… the fact that most hazards remain "TOLERABLE" (not

"NEGLIGIBLE") means that it is not a panacea and still has

shortcomings in areas such as vertical navigation. It is

recommended that work continues to address these

shortcomings …”

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Benefits of RNAV

27

The change in navigation

28

Before RNAV

29

After RNAV

30

RNAV vs RNP

• “RNAV” means the aircraft can follow a pre-defined

track with 1 NM accuracy 95% of the time

• “RNP” means the aircraft can follow a pre-defined

track with 1 NM accuracy 95% of the time AND there is

on-board monitoring and alerting that warns the pilot if

accuracy is insufficient

1 Nautical Mile 95% of flight time

1 Nautical Mile 95% of flight time

Track Centerline

For example, RNAV 1:

31

Navigation errors

• Lateral navigation errors (95% of flight time)

• Characterized by the Total System Error (TSE)

Desired Path

Defined Path

Estimated position

Actual position

Path Definition Error Flight Technical Error

Navigation

Sensor

Error

Total

System

Error

TSE is the Root Sum Square (RSS) of 3 errors: PDE, NSE and FTE

The navigation accuracy the aircraft achieves in practice is known

as the Actual Navigational Performance (ANP) 32

So what work has been completed for helicopters

to date?

• Focus on GNSS implementations to date have been

mostly fixed wing

MIELEC 33

The SBAS Offshore Approach Procedure (SOAP)

35

Straight approach – no turning / Vertical guidance

SOAP offers several significant advantages

• Less reliance on weather radar (combined with AIS)

• Independent cross-check against existing altimeters

• Allows a “straight in” procedure from final to missed

approach

• Enables autopilot to lower crew workload

• High navigation accuracy

36

Developed as a safety enhancement to current

procedures

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What about the integrity

of the GNSS signal for

helicopters?

37

Reception of GNSS signals affected more on

rotorcraft

• EGNOS GEOs broadcast SBAS correction message at a

low elevation angle in the operating areas

• Suggests the EGNOS signal may be more vulnerable to

masking and rotor interference than GPS

• Due to its lower specified maximum and typical power levels

• GPS presently radiates well above the specified level

• Structural limitations mean less options of mounting

GNSS antenna

38

CAA PAPER 2003/7 - Effect of Helicopter Rotors on

GPS Reception

North Sea EGNOS reception tests

39

The ‘test’ rig

40


42

Helicopter pitch and roll angles during flight

-20

-10

0

10

20

30

40

483,500 484,000 484,500 485,000 485,500 486,000

GPS seconds in week

Pit

ch/R

oll

An

gle

(d

eg)

Pitch

Roll

PRN120

PRN124

PRN126

Taxi-out Take off Orbits Approaches Final approach, landing & taxi to stand

Pitch up

on take

off

Consecutive loss of Geos during orbit


43

Helicopter heading during flight trial

0

90

180

270

360

483,000 483,500 484,000 484,500 485,000 485,500 486,000

GPS seconds in day

Magn

etic

hea

din

g (

deg

)

Hdg

PRN120

PRN124

PRN126

Validation of the signal under HEDGE

• Under HEDGE further analysis of EGNOS reception:

• 485 flights = 689 hours, 15 minutes and 44 seconds of flight

• 127 hours of recorded data on different SBAS receivers

• 4,591,662 points analysed

44

Validation of the signal under HEDGE

45

Vertical Standford Plot Horizontal Standford Plot

SOAP equipment integration

Back-end pallet

AIS receiver

GNSS receiver

Development and logging laptop

ARINC 429

serial

converter

47

Flight crew installation

Instrument display

Blanking plate

48

On-board installation

Rear pallet installed

Flight crew display

installed

50

Flight crew display

51

Flight trials

Flight schedule approaches

Flight # Approach # Descent slope Wind LDG/GA Approach #

1

1 4° Into GA Data lost

2 6° Out of GA 1444

3 4° Out of LDG 1459

4 Pilot choice Pilot choice Pilot choice 1513

2

1 4° Into GA Data lost

2 6° Out of GA 1024



3

1 4° Into GA 1322

2 6° Out of GA 1334



53

Lateral path deviations

0

50

100

150

200

250

1 7

13

19

25

31

37

43

49

55

61

67

73

79

85

91

97

103

109

115

121

127

133

139

145

151

157

163

169

175

181

187

193

199

205

211

217

223

229

235

241

247

253

259

265

271

277

283

289

295

301

Erro

r in

me

tre

s

1024 1039 1058 1322 1334 1353 1407 1444 1459 1513

54

Vertical path deviations

0

10

20

30

40

50

60

70

1 7

13

19

25

31

37

43

49

55

61

67

73

79

85

91

97

103

109

115

121

127

133

139

145

151

157

163

169

175

181

187

193

199

205

211

217

223

229

235

241

247

253

259

265

271

277

283

289

295

301

Erro

r in

me

tre

s

1024 1039 1058 1322 1334 1353 1407 1444 1459 1513

55

Flight path errors

• Lateral deviations

• Vertical deviations

1444 1459 1513 1024 1039 1058 1322 1334 1353 1407 Overall

Mean 30.79 56.64 34.97 49.18 27.97 10.87 33.45 8.06 15.73 11.91 26.93

Max 88.53 230.19 164.36 150.07 121.94 60.11 72.97 42.27 48.80 23.05 230.19

Standard

deviation23.49 72.35 38.20 45.60 26.36 7.90 18.80 7.58 13.29 6.36 35.22

1444 1459 1513 1024 1039 1058 1322 1334 1353 1407 Overall

Mean 17.03 11.77 11.03 9.03 9.54 12.88 9.10 9.97 10.12 18.26 11.80

Max 65.97 25.48 28.75 23.60 20.95 24.30 19.07 27.25 36.71 33.28 65.97

Standard

deviation20.39 7.51 7.63 6.58 7.03 6.89 5.14 8.55 11.90 9.37 10.01

Overall

26.93

230.19

35.22

Overall

11.80

65.97

10.01

56

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Future development

57

HMI changes to aid manual descent

58

HMI aid to level off anticipation in manual descent

59

SOAP has successfully validated and continues to

be improved

• Flight crew agreed that SOAP is more precise than

existing low visibility options

• Horizontal and vertical track keeping is precise but

increases crew workload

• Coupling with autopilot required

• Further work in the area will be undertaken

• UK CAA sponsoring HMI enhancements and additional flight

trials

60

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Thank you for your attention

[email protected]

Helicopter precision approaches using GNSS

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