- 1 Approach
The supporting flight tests to show compliance with CS AWO.B.CATIII.115(a) in respect of approach performance may be a programme of flight demonstrations carried out in accordance with AMC AWO.B.CATII.113.
- 2 Touchdown
For compliance with CS AWO.B.CATIII.115(b) in respect of touchdown performance, a programme of flight demonstrations will be required to support the simulation and analysis. (See AMC AWO.A.ALS.106)
- 3 Ground roll
- 3.1 A programme of landings should be carried out to ensure that there is a confidence level of 90 % that the criterion of CS AWO.B.CATIII.117(a) is complied with. This programme and the analysis of the results should be in accordance with the procedures established for approach performance. (See AMC AWO.B.CATII.113 paragraph 2)
- 3.2 When operation is based on fail-operational ground roll, a programme of flight demonstration landings is necessary to support the simulation and the analysis programme which are required to demonstrate compliance with CS AWO.B.CATIII.117(b). (See AMC AWO.A.ALS.106)
ED Decision 2022/007/R
4 Considerations for GLS
- 4.1 Compatibility with rare undetected non-aircraft system error conditions (See Appendix 1 to AMC to Subpart A)
The criteria below establish the compatibility of the ICAO standardised ground monitoring performance for satellite faults and single ground-reference receiver faults with the aircraft performance including satellite geometry screening. The criteria ensure that undetected faults or rare normal errors in non-aircraft GBASs, when combined with all other nominal factors that affect landing performance, do not result in an unacceptably high probability of landing outside the limits that define a safe landing.
Note: Appendix 1 to AMC AWO.B.CATIII.115 GBAS performance model for approach and landing simulation contains a list of references that have been used to derive the signal model. These references describe undetected non-aircraft system error conditions, rare normal performance and faults as well as the ICAO standardised ground system monitoring requirements. The aircraft requirements in this Section are intended to address non-aircraft system errors that are below the ground monitoring thresholds. The existence of such errors is not considered a malfunction of the non-aircraft system.
For any value of GLS NSE, including the effects of undetected satellite faults and undetected faulted conditions at a single ground-reference receiver, it must be shown that the touchdown performance will be such that the exceedance of any of the limits prescribed in CS AWO.A.ALS.106(c) will be less than those prescribed in AMC AWO.A.ALS.106 paragraph 1.4 for the limit condition.
Other non-GLS variables that effect performance shall vary according to their expected distributions when assessing this compatibility. Credit for the prior probability of the fault cannot be taken when evaluating the required landing probabilities; however, credit may be taken for the ground subsystem's probability of detection for satellite faults and the aircraft's probability of detection for single -reference receiver faults.
Note: It is assumed that operations will be approved with knowledge of the runwayspecific glide path and threshold crossing height values and the aircraft's capability. Therefore, it is not necessary to determine compliance with this Section using the glide path and threshold crossing height values set to the limit allowed for the aircraft.
4.2 Compatibility with worst-case undetected guidance errors
Rare ionosphere events and undetected satellite or ground station failures could result in significant vertical (and lateral) position errors. Under certain conditions, such errors may go undetected by the system and could result in erroneous guidance if not mitigated. The effect of such errors may not be observable by the flight crew.
All undetected errors that are not extremely improbable shall not prevent a safe landing and/or go-around when all other variables that effect the performance are at their nominal values. The effect of worst-case undetected errors on landing system performance shall be assessed via simulation using the GLS noise model provided in Appendix 1 to AMC to Subpart A. The worst-case undetected errors shall be simulated by using the maximum range domain error given in Table 5 of Appendix 1 to AMC to
Easy Access Rules for All-Weather Operations (CS-AWO)
SUBPART B -APPROACH AND LANDING SECTION 4 -AIRWORTHINESS CERTIFICATION OF AEROPLANES FOR OPERATIONS WITH DECISION HEIGHTS (DHs) BELOW 30 M (100 FT) OR NO DECISION HEIGHT (DH) -CATEGORY III (CAT III) OPERATIONS
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Subpart A in conjunction with the appropriate geometry screening factors used by the aircraft. The certification plan must specify how the demonstration will be conducted, including the number of cases and variables with pass -fail criteria. The aeroplane performance shall be assessed in the presence of the full range of bias and ramp type failures produced by the fault mode generator described in Appendix 1 to AMC to Subpart A.
[Issue: CS-AWO/2]
APPENDIX 1 TO AMC AWO.B.CATIII.115 Performance demonstrations
1 Limit case analysis
Demonstration of compliance with paragraph 4.1 of AMC AWO.B.CATIII.115 may be done by analysis to show that for all possible sizes of navigation error, the joint probability that the error is not detected and that the error results in the aeroplane landing outside the safe landing box as defined in CS AWO.A.ALS.106 is less than 1 × 10 -5 . The analysis uses the nominal touchdown distributions (lateral and longitudinal) along with the geometry factors (Svert and Slat), and the maximum allowable Pmd performance of the monitors for satellite ranging source failures and for the reference receiver fault monitor (RRFM). The nominal touchdown distribution is used to compute the probability of an unsuccessful landing given a particular size of error 𝑃 𝑈𝐿|𝐸 (𝐸) . This probability is then multiplied by the probability of an error not being detected as a function of E, Pmd(E). The probability of an unsuccessful landing given in error is the joint probability that the fault that causes an error, E, is not detected and the landing will be unsuccessful given an error, E:
<!-- formula-not-decoded -->
To form the conditional unsuccessful landing probability , 𝑃 𝑈𝐿|𝐸 (𝐸) , a conditional touchdown distribution should be used that would result from a constant bias error in addition to the faultfree NSE and flight technical error distributions. This should be done for the full range of relevant error sizes to form the total conditional probability of an unsuccessful landing as a function of the error. The conditional unsuccessful landing probability is expressed as follows for the land-short and land-long cases:
Land short
<!-- formula-not-decoded -->
<!-- formula-not-decoded -->
<!-- formula-not-decoded -->
Land with wheels less than 5 ft from the edge of the runway:
<!-- formula-not-decoded -->
where:
LSC is the land-short criteria (i.e. 200 ft);
LLC is the land-long criteria (i.e. 3 000 ft);
RWE is the lateral landing criteria (i.e. 70 ft);
ED Decision 2022/007/R
GW is the lateral distance between the main landing gear;
pTSE\_LON|E (x, E) is the probability density function for the longitudinal touchdown given a bias of magnitude E; and
pTSE\_LAT|E (x, E) is the probability density function for the lateral touchdown given a bias of magnitude E.
Note: Care should be taken to ensure consistency of units when making these calculations.
1.1 Computing Pmd for ranging source errors
A bound on the probability of missed detection for the ranging source error, 𝑃𝑚𝑑 (𝐸 𝑅 ) , is defined by the performance constraint region given in ICAO Annex 10 Appendix B Section 3.6.7.3.3.2. The Pmd performance should lie below the curve defined by Table B-76A in the SARPs, repeated here for convenience.
Table B-76 A: Pmd\_limit parameters
| Probability of missed detection | Pseudo-range error (metres) |
|---|
| P md_limit ≤ 1 | 0 ≤ |E r | < 0.75 |
| P md_limit 10 ( - 2.56 ×|Er| + 1.92) | 0.75 ≤ |E r | < 2.7 |
| P md_limit 10 - 5 | 2.7 ≤ |E r | < |
For example, in the case of the longitudinal touchdown requirement, the vertical position error has the largest effect on the touchdown location. The worst-case projection of a range error into vertical error, max(|SAprvert.i |) , may be used to determine the resulting limit on 𝑃𝑚𝑑 (𝐸 𝑉 ) by substituting ER = 𝐸𝑉 max(|SAprvert.i |) / .
Figure 1 illustrates the relationship between Pmd\_limit and the 𝑃𝑚𝑑 (𝐸 𝑉 ) for max(|SAprvert.i |) = 5.
MEASA
10°
Pmd Range to Position Domain given SvertMax=5
102
108
10:10
0
Figure 1: Example of the satellite ranging source Pmd in the range domain and position domain
- 1.2 Computing Pmd for reference receiver fault monitoring
The Pmd for the RRFM is given by:
<!-- formula-not-decoded -->
where:
BAC T is the maximum threshold for the RRFM monitor given by:
<!-- formula-not-decoded -->
where:
VAL is the vertical alert limit that is used by airborne equipment to screen geometry expressed in metres.
And pBmd(x,EV) is the probability density function (pdf) of | Bj,vert (EV) | in the faulted circumstance given by:
Easy Access Rules for All-Weather Operations (CS-AWO)
SUBPART B -APPROACH AND LANDING SECTION 4 -AIRWORTHINESS CERTIFICATION OF AEROPLANES FOR OPERATIONS WITH DECISION HEIGHTS (DHs) BELOW 30 M (100 FT) OR NO DECISION HEIGHT (DH) -CATEGORY III (CAT III) OPERATIONS
<!-- formula-not-decoded -->
where dnorm(x, , ) is the Gaussian pdf
<!-- formula-not-decoded -->
For a derivation of these expressions, see reference [ 1 ] of Appendix 1 to AMC to Subpart A.
1.3 Example assessments
Figure 2 illustrates a landing-short assessment for a hypothetical aeroplane with a nominal longitudinal touchdown point of 1 500 ft from the threshold and a dispersion that can be bounded by a Gaussian distribution with σ = 220 ft. Also, a max(|SAprvert.i |) of 5, VAL of 10 metres and GPA of 3 degrees is used. Rearranging equation [1]:
<!-- formula-not-decoded -->
Hence, by dividing 10 -5 by the Pmd curves for satellite ranging sources and RRFM, the grey 'keep -out regions' shown in Figure 2 can be obtained. The assessment is then simple. If the curve for 𝑃𝑈𝐿|𝐸 (𝐸) does not enter the keep-out regions, then the requirement that 𝑃𝑈𝐿 (𝐸) < 10 -5 is met for all values of E.
An alternative approach to the analysis is illustrated in Figure 3 where the probability of an unsuccessful landing is explicitly calculated for both monitor types (ranging sources and RRFM).
Extension of these examples to the land-long and lateral cases is straightforward.
1 ICAO Standards and Recommended Practices (SARPs) for the Global Navigation Satellite System (GNSS). Annex 10 to the Chicago Convention, Vol 1.
10°
MEASA
Probability of an Unsuccessful Landing Given E, - Landing Short
10'
10?
103
· 10%
- 5
10
10€
10'
108
Fiaure 2: Example assessment of landina-short performance
Figure 2: Example assessment of landing-short performance
10°
MEASA
Probability of an Unsuccessful Landing Given E, - Landing Short
10°
Probability
10'1°
1015
10:20
Fiaure 3: Explicit calculation of PUL for the land-short example above
Figure 3: Explicit calculation of PUL for the land-short example above
[Issue: CS-AWO/2]