A Review of CAT II-III LAAS Integrity Requirements and their .ppt

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1、,A Review of CAT II/III LAAS Integrity Requirements and their Antecedents,Stanford GPS Laboratory Group Meeting 4 August 2006,Sam Pullen Stanford University (with lots of help from Tim Murphy of Boeing),4 August 2006,CAT II/III Integrity Requirements and Antecedents,2,English Word of the Day,Anteced

2、ent: (Webster online dictionary) 1 : a substantive word, phrase, or clause whose denotation is referred to by a pronoun (as John in “Mary saw John and called to him“); broadly : a word or phrase replaced by a substitute grammar only 2 : the conditional element in a proposition (as if A in “if A, the

3、n B“) grammar only 3 : the first term of a mathematical ratio rarely used 4 a : a preceding event, condition, or cause b plural : the significant events, conditions, and traits of ones earlier life very general 5 a : PREDECESSOR; especially : a model or stimulus for later developments b plural : ANC

4、ESTORS, PARENTS,4 August 2006,CAT II/III Integrity Requirements and Antecedents,3,Presentation Outline,Review of LAAS Precision Approach Requirements Antecedents of these requirements: ICAO Annex 10 Requirements for ILS FAA AC 25.1309 and AC 120-28D wording FAA Hazard Risk Index table Total Aircraft

5、 Safety sub-allocation What should the “real” be, and how should it be derived? Some initial thoughts,Precision Approach Requirements in Updated LAAS MASPS (RTCA DO-245A, December 2004),4 August 2006,CAT II/III Integrity Requirements and Antecedents,5,GBAS Service Level (GSL) Definitions,Table 1-1 (

6、Section 1.5.1) of DO-245A,4 August 2006,CAT II/III Integrity Requirements and Antecedents,6,GSL Requirements Table,Table 2-1 (Section 2.3.1) of DO-245A,Antecedents of Precision Approach Requirements 1: FAA Hazard Risk Index,Useful reference: Ch. 3 of FAA System Safety Handbook (12/30/00) http:/www.f

7、aa.gov/library/manuals/aviation/risk_management/ss_handbook/media/Chap3_1200.PDF,4 August 2006,CAT II/III Integrity Requirements and Antecedents,8,Cat III,FAA Risk Severity Classifications*,Minor: failure condition which would not significantly reduce airplane safety, and which involve crew actions

8、that are well withintheir capabilitiesMajor: failure condition which would significantly:(a) Reduce safety margins or functional capabilities of airplane(b) Increase crew workload or conditions impairing crew efficiency(c) Some discomfort to occupantsSevere Major (“Hazardous” in ATA, JAA): failure c

9、ondition resultingin more severe consequences than Major:(a) Larger reduction in safety margins or functional airplane capabilities(b) Higher workload or physical distress such that the crew could not be relied upon to perform its tasks accurately or completely(c) Adverse effects on occupantsCatastr

10、ophic: failure conditions which would prevent continued safeflight and landing (with probability 1),* Taken from AC No. 25.1309-1A, AMJ 25.1309, SAE ARP4761 (JHUAPL summary),Cat I,4 August 2006,CAT II/III Integrity Requirements and Antecedents,9,FAA Hazard Risk Index (HRI) Table,Cat. I ILS case,Cat.

11、 III ILS case,Several versions exist, all with essentially the same meaning Source of this version: 1999 Johns Hopkins Applied Physics Laboratory “GPS Risk Assessment Study” final report http:/www.faa.gov/asd/international/GUIDANCE_MATL/Jhopkins.pdf,Antecedents of Precision Approach Requirements 2:

12、FAA Advisory Circulars Defining Certification and Airworthiness Criteria,For AC 25.1309-1A, “System Design and Analysis,” 6/21/88:http:/www.airweb.faa.gov/Regulatory_and_Guidance_Library%5CrgAdvisoryCircular.nsf/0/50BFE03B65AF9EA3862569D100733174?OpenDocument For AC 120-28D, “Criteria for Approval o

13、f Category III Weather Minima for Takeoff, Landing, and Rollout,” 7/13/99:http:/www.airweb.faa.gov/Regulatory_and_Guidance_Library%5CrgAdvisoryCircular.nsf/0/BBADA17DA0D0BBD1862569BA006F64D0?OpenDocument,4 August 2006,CAT II/III Integrity Requirements and Antecedents,11,Key Elements of AC 25.1309-1A

14、,AC 25.1309-1A is the primary basis for safety certification within the FAA AC 25.1309-1A specifies a “fail-safe” policy (quote): In any system or subsystem, the failure of any single element, component, or connection during any one flight (e.g., brake release through ground deceleration to stop) sh

15、ould be assumed, regardless of its probability. Such single failures should not prevent continued safe flight and landing, or significantly reduce the capability of the airplane or the ability of the crew to cope with the resulting failure conditions. Subsequent failures during the same flight, whet

16、her detected or latent, and combinations thereof, should also be assumed, unless their joint probability with the first failure is shown to be extremely improbable. AC 25.1309-1A defines the likelihood and severity terms found in the Hazard Risk Index Provides guidance as to what factors can be take

17、n credit for in probability assessments and how this should be done Refers to RTCA DO-178 for software safety assurance guidance More recent SAE standards (ARP 4754 and 4761) provide much more detailed guidance on FAA safety-assurance methods,4 August 2006,CAT II/III Integrity Requirements and Antec

18、edents,12,Summary of CAT III Airworthiness Requirements (Table from Tim Murphy of Boeing),Tim Murphys presentation is inside RTCA SC-159 WG-4 Archive File: http:/sc159.tc.faa.gov/wg4/060706/Jun072006.htm,4 August 2006,CAT II/III Integrity Requirements and Antecedents,13,CAT III Touchdown Zone (or “B

19、ox”),Figure from Figure 3 of Tim Murphys requirements report to FAA: Boeing Doc. # D6-83447-4, 10/19/05 Numbers taken from App. 3, Section 6 of FAA AC 120-28D,Additional “bank angle hazard” requirement limits probability of any part of wing or engine touching ground to 10-7 or less,4 August 2006,CAT

20、 II/III Integrity Requirements and Antecedents,14,Translation of Touchdown Zone into Landing System Requirements,Provided in ICAO Annex 10 for ILS (April 1985) not available online Annex 10 was amended for MLS and is being amended for GBAS Amendment 79 is latest (?) Annex 10 specifies 95% accuracy l

21、imits and monitor limits in terms of ILS measurements (DDM) Translation to LAAS required knowledge or assumption of several non-obvious intermediate parameters In my understanding, ILS requirements in Annex 10 were designed around already-fielded ILS systems that were already deemed to be safe CAT I

22、II guidance requirements were not much more strict main difference was tighter, higher-reliability monitoring needed,Antecedents of Precision Approach Requirements 3: Example Risk Allocations,Source: R.J. Kelly, J.M. Davis, “Required Navigation Performance (RNP) for Precision Approach and Landing wi

23、th GNSS Application,” Navigation, Vol. 41, No. 1, Spring 1994, pp. 1 30. http:/www.ion.org/search/view_abstract.cfm?jp=j&idno=106,4 August 2006,CAT II/III Integrity Requirements and Antecedents,16,Breakdown of Worldwide Accident Causes: 1959 - 1990 (from ICAO Oct. 1990 Study),Total hull loss probabi

24、lity per flight (“mission”) as of 1990 = 1.87 10-6 Current probability per commercial departure in U.S. = 2.2 10-7 (3-year rolling average last updated in March 2006) http:/faa.gov/about/plans_reports/Performance/performancetargets/details/2041183F53565DDF.html,4 August 2006,CAT II/III Integrity Req

25、uirements and Antecedents,17,U.S. Accident Breakdown by Cause (2000-01),2001,2000,From NSTB Annual Review of Aircraft Accident Data, 2000 and 2001; ARC 04/01; 06/01 http:/www.ntsb.gov/publictn/A_Stat.htm,4 August 2006,CAT II/III Integrity Requirements and Antecedents,18,Semi-unofficial “Serious Acci

26、dent” Risk Allocation (proposed in 1983 SAE paper),D.L. Gilles, “The Effect of Regulation 25.1309 on Aircraft Design and Maintenance,” SAE Paper No. 831406, 1983.,Total Serious Accident Risk,Numbers based on approximations of observed accident history.,10-6 per flight hour,All Other Causes (human er

27、ror, weather, etc.),9 10-7 p. f. hr.,90%,10%,Aircraft System Failures (engines, control, avionics, etc.),1 10-7 p. f. hr.,Assume 100 sepa-rate aircraft systems,Each individual system is allocated 1 10-9 p. f. hr. (or per flight).,Not subject to certification; thus not broken down in detail here.,How

28、 should the “real” CAT II/III requirements (and other aviation safety requirements) be determined (work in progress )?,4 August 2006,CAT II/III Integrity Requirements and Antecedents,20,Weaknesses in Current Safety Approach,No clear means to adapt safety requirements to continued improvement in over

29、all aircraft safety 10-9 requirement per individual aircraft system appears to be out-of-date given that current overall serious accident risk is approaching 10-7 per flight 10-6 probability for landing in CAT III touchdown zone seems dated No clear means to appropriately balance rare-event probabil

30、ities 10-9 qualifies as “extremely improbable”, but 5 10-9 only qualifies as “improbable” and must be treated as “latent” with probability 1 according to strict reading of AC 25.1309-1A No means to “trade off” safety benefit vs. safety risk for new systems that, when working properly, reduce the ris

31、k of accidents caused by pilot/weather/ATC/etc. Most new systems, including SBAS and GBAS, likely retire more pilot/weather/ATC risk than they introduce due to the possibility of their own failure,4 August 2006,CAT II/III Integrity Requirements and Antecedents,21,FAA Safety Engineering Tries to Adap

32、t,FAA shows no interest in fundamentally changing current certification standards Instead, FAA reacts to accidents on a case-by-case basis and tries to change individual rules interpretations subtly and quietly New interpretations also apply to new systems, such as SBAS and GBAS Example 1: aircraft

33、rolling out long and off runway (recent SWA 737 accident at Midway) FAA now promulgating requirements “clarification” mandating a specific 15% runway margin; see: http:/ August 2006,CAT II/III Integrity Requirements and Antecedents,22,FAA Safety Engineering Tries to Adapt (2),Example 2: TWA 800 (Jul

34、y 1996) 747 explosion most likely caused by ignition of center fuel tank NTSB accident report (August 2000): http:/www.ntsb.gov/publictn/2000/AAR0003.pdf Many small fuel-tank risk- reduction steps implemented under SFAR 88 beginning in 2001 Major ignition-suppression retrofit proposed in Notice of P

35、roposed Rule Making (NPRM; Nov. 2005) http:/dmses.dot.gov/docimages/pdf94/373450_web.pdf Lengthy technical and cost-benefit debate on this NPRM continues to this day; see: http:/dmses.dot.gov/docimages/pdf94/373645_web.pdf http:/dmses.dot.gov/docimages/pdf95/389033_web.pdf,4 August 2006,CAT II/III I

36、ntegrity Requirements and Antecedents,23,FAA Safety Engineering Tries to Adapt (3) (Continuation of Example 2: TWA 800 Accident),Previous certification of fuel tank safety relied on need for multiple triggering events to occur joint probability was below 10-9 per flight However, initiating event cou

37、ld lie undiscovered for many flights prior to being detected by periodic maintenance New FAA “specific risk” concept requires that “knowable” latent defects be treated as present with probability 1 Thus, 10-9 mitigation argument no longer holds in this case Also, undetected latent failure could leav

38、e aircraft only one failure away from “catastrophic” incident FAA and manufacturers have been debating this application of “specific risk” since 2002; see: https:/www.faa.gov/regulations_policies/rulemaking/committees/arac/minutes/media/TAE_OCT_05.pdf http:/edocket.access.gpo.gov/2006/pdf/E6-4024.pd

39、f,4 August 2006,CAT II/III Integrity Requirements and Antecedents,24,Summary,A complex set of requirements and guidance documents links todays CAT II/III landing requirements to overall FAA safety objectives As CAT II/III requirements are refined to be more “GBAS-specific,” re-thinking of the intent

40、 of the antecedents of these requirements is important FAA safety requirements evolution is limited in scope and is limited to “new” systems like SBAS and GBAS and response to external events, e.g., accidents Further changes to better reflect improved overall aircraft safety and safety contribution

41、of newer systems would be desirable,4 August 2006,CAT II/III Integrity Requirements and Antecedents,25,Backup Slides Follow,4 August 2006,CAT II/III Integrity Requirements and Antecedents,26,Integrity Requirement Definitions,Integrity relates to the trust that can be placed in the information provid

42、ed by the navigation system Misleading Information (MI) occurs when the true navigation error exceeds the appropriate alert limit (an unsafe condition) without annunciation Time-to-alert is the time from when an unsafe condition occurs to when the alarm message reaches the pilot (guidance system) A

43、Loss of Integrity (LOI) event occurs when an unsafe condition occurs without annunciation for a time longer than the time-to-alert limit, given that the system predicts it is available,4 August 2006,CAT II/III Integrity Requirements and Antecedents,27,Notes to GSL Requirements Table,Section 2.3.1 of

44、 DO-245A,1. The values given for GNSS accuracy and alert limits are those required for the intended operation at the lowest height above threshold (HAT) where the GNSS guidance is relied upon. 2. The definition of the integrity requirement includes an alert limit and a time to alert, against which t

45、he requirement can be assessed. 3. The accuracy requirements include the nominal performance of a fault-free airborne subsystem. 4. The integrity requirements are specified in terms of a probability to be evaluated over a specified period. The duration of this period is intended to correspond to the

46、 most critical portion of an approach & landing for the operations the GSL is intended to support. Integrity risk includes the probability of latent failures, and the exposure time to these types of failures may exceed the specified period, therefore the requirement must apply during “any” period. N

47、ote that if the integrity requirements for GSL D-F are met, the integrity requirements for GSL A-C are also automatically met. 5. For these GSLs (D, E, and F), the combined lateral and vertical risk shall not exceed 1 10-9, where the risk for vertical applies over any 15 sec, and the risk for latera

48、l applies over any 30 sec. The lateral period is longer because these GSLs are intended to support operations that require LAAS guidance during roll-out. 6. The time-to-alert (TTA) is the maximum time between the onset of a failure condition that affects the integrity of any information that could b

49、e applied by the airborne subsystem and the time that the alert indication is available at the output of the airborne subsystem, where the airborne subsystem is assumed to have zero latency. Compliance with the TTA requirement must include consideration of the probability of missed VDB messages by a fault-free airborne subsystem.,4 August 2006,CAT II/III Integrity Requirements and Antecedents,28,Actual “Hull Loss” Probability Breakdown (from October 1990 ICAO Study Data),