Operational Liaison Meeting Fly-By-Wire Aircraft

2004

TCAS Recommendations

Customer Services

Contents
Introduction TCAS Presentation Resolution Advisory Review of TCAS Events Recurrent TCAS Questions
AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.

Future TCAS Developments Conclusion

TCAS - Recommendations
Page 2

Introduction
Each year, numerous reports reveal that mid-air collisions are
avoided by a whisker.

Air Traffic Controllers (on ground) strive to avoid such events. The onboard Traffic Collision Avoidance System (TCAS)
was developed to prevent mid-air collision, particularly in case Air Traffic Controller guidance is incorrect.

TCAS II has become mandatory:

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4Since

1986, in the US 4Since 2000, in Europe

TCAS II has a worldwide ICAO mandate as January 1st, 2003.

TCAS - Recommendations
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Contents
Introduction TCAS Presentation Resolution Advisory Review of TCAS Events Recurrent TCAS Questions
AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.

Future TCAS Developments Conclusion

TCAS - Recommendations
Page 4

TCAS Presentation
Basic TCAS Principles
TCAS:

Detects any nearby aircraft that is equipped with an

ATC Transponder.

Displays potential collision targets.

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Triggers vertical orders to avoid conflict.

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TCAS Presentation
Basic TCAS Principles

Interrogation TCAS II Reply Mode S Address - Altitude

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MODE S XPDR

Interrogation MODE S XPDR TCAS II Reply Mode S Address - Altitude

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TCAS - Recommendations

TCAS Presentation
Basic TCAS Principles
TCAS calculates the:

Bearing (based on the direction of the received signal) Range (based on the time that the signal was received) Trajectory and speed (based on intruder position evolution)
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Relative Altitude (based on the signal received)

TCAS - Recommendations

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TCAS Presentation
Basic TCAS Principles
OTHER VOLUME PA VOLUME

TA VOLUME RA VOLUME

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TCAS - Recommendations

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TCAS Presentation
TCAS Display

RA located 300 feet above and descending

-5

+3

TA located 500 feet below and climbing

+12

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PROXIMATE located 1200 feet above and descending OTHER located 1500 feet below and climbing

-15

TCAS - Recommendations

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Contents
Introduction TCAS Presentation Resolution Advisory Review of TCAS Events Recurrent TCAS Questions
AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.

Future TCAS Developments Conclusion

TCAS - Recommendations
Page 10

Resolution Advisory
Background

Amidst all the TCAS information, the

most important involves Resolution Advisories.

TCAS calculates two types of

Resolution Advisories (RA):
4Preventive
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Advisory ( MAINTAIN

VERTICAL SPEED MAINTAIN): Red sector appears on V/S scale, the V/S needle is in the grey area. The red square is displayed on the Navigation Display. No pilot action on the sidestick (maintain the current vertical speed).

TCAS - Recommendations

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Resolution Advisory
Background
4Corrective

Advisory:

The vertical speed needle is in the red area. The red square is displayed on the Navigation Display

4Follow 4Follow
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aural warnings.

vertical speed green sector on the PFD.

TCAS - Recommendations

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Resolution Advisory
Background
4Corrective

Advisory (e.g. ADJUST VERTICAL SPEED,

ADJUST):
TCAS computes the best avoidance maneuver according to a model:

Assumes pilots reaction within 5 seconds and accelerates with

0.25g in climb or descent until +/-1500 ft/min is reached V/S must be maintained until clear of conflict.
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Smoothly and firmly follow green sector within 5 seconds

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Resolution Advisory
Background
4Corrective

Advisory
TAU TAU

Vertical miss distance ADJUST VERTICAL SPEED, ADJUST CPA (Closest Point of Approach)
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Generally: Deviation caused by a RA maneuver is between 300 and 500 ft Vertical miss distance at the Closest Point of Approach is around 400 ft

TCAS - Recommendations

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Resolution Advisory
Background
4Corrective

Advisory
TAU TAU

Relative altitude ADJUST VERTICAL SPEED, ADJUST CPA (Closest Point of Approach)
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Do not overreact Do not disregard a weakening RA It could create another conflict with another aircraft
TCAS - Recommendations
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Resolution Advisory
Background
4Additional

Corrective Advisory (E.g.: INCREASE DESCENT)

TCAS computes the best avoidance maneuver according to a model:

Assumes pilots reaction within 2.5 seconds and accelerates with

0.35g in climb or descent until +/-2500 ft/min is reached V/S must be maintained until clear of conflict.

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Firmly follow green sector within 2.5 seconds

TCAS - Recommendations

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Resolution Advisory
Evolution of RA Alerts

The following diagram illustrates the number and

evolution of RA alerts since 1999 ( Based on Eurocontrol source) :
3500 3000 2500 2000
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1500 1000 500 0 1999 2000 2001 2002 2003

TCAS - Recommendations

RAs alerts

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Resolution Advisory
Evolution of RA Alerts

Statistics in Europe for 2000 ( Based on Eurocontrol source)

35 30 25 20
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15 10 5 0
Takeoff Climb Cruise Descent HLD Approach Final Approach

RAs repartition

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Resolution Advisory
Evolution of RA Alerts

Statistics in Europe for 2000 ( Based on Eurocontrol source)

4Pilots

followed RA in 95% of reported cases 4Decision not to follow an RA was based on additional information: Intruder visually acquired Traffic information and/or ATC avoidance being issued by ATC.
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TCAS - Recommendations

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Resolution Advisory
Evolution of RA Alerts
2003 results are incomplete: 4Still missing information from some countries

Globally, however, the number of alerts is decreasing:

4Less

reports from pilots 4The introduction of TCAS Change 7 reduces the number of RAs by a factor of 2.
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However, since there are still a significant number of RAs:

Pilots must be well-trained and informed on how to react when faced with an RA TCAS order.
TCAS - Recommendations
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Contents
Introduction TCAS Presentation Resolution Advisory Review of TCAS Events Recurrent TCAS Questions
AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.

Future TCAS Developments Conclusion

TCAS - Recommendations
Page 21

Review of TCAS Events

Background
The previously-shown TCAS figures, includes cases where TCAS RA orders were not always followed.

Some such cases have been reported, and include:

4Various

missed mid-air collisions. 4The tragic Constance Lake event of July 1st 2003.
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Always follow TCAS RA orders, even if not in accordance with ATC orders.

TCAS - Recommendations

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Review of TCAS Events

Event N 1
Aircraft 1 and Aircraft 2 were both at FL 70. Aircraft 2 was instructed, late, to descend to FL60.
The distance between Aircraft 1 and Aircraft 2 is 5 NM

The TCAS triggered coordinated RAs:

4DESCEND, DESCEND RA order for Aircraft 4CLIMB, CLIMB RA order for Aircraft 2

Aircraft 2
4Followed the ATC order (Descend 4But, NOT the TCAS order.
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to FL 60)

Aircraft 1
4Followed

the INCREASE DESCENT, INCREASE DESCENT TCAS order.

This induced a new TCAS conflict with Aircraft 3 at FL 50 .

TCAS - Recommendations
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Review of TCAS Events

Event N 1
FL 70 AIRCRAFT 1
DESCEND, DESCEND RA CLIMB, CLIMB RA

AIRCRAFT 2
INCREASE DESCENT, INCREASE DESCENT RA

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FL 50

AIRCRAFT 3
AIRCRAFT 2 descend FL 60.

Simultaneous vertical and horizontal crossing at less than 1 NM

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Review of TCAS Events

FCOM Update

The FCOM has been slightly revised to further emphasize

the fact that pilots must follow the TCAS order:

The previous FCOM 3.04.34 page:

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New FCOM 3.04.34 page (January Revision):

TCAS - Recommendations

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Review of TCAS Events

Event N2

Aircraft 1: Was approaching FL 260 Aircraft 2: Was cruising at FL 270 Aircraft 1:

4Received

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an ADJUST VERTICAL SPEED, ADJUST RA. 4Reacted by increasing, rather than decreasing, the vertical speed. 4Reached FL 271, before returning to FL 260

Aircraft 2:
4Received

and followed a CLIMB, CLIMB RA.

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TCAS - Recommendations

Review of TCAS Events

Event N2
CLIMB, CLIMB RA

FL 270
AIRCRAFT 2 AIRCRAFT 1
ADJUST VERTICAL SPEED, ADJUST RA
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FL 260

Minimum crossing margin: 300 feet, 0.8 NM!!!

TCAS - Recommendations
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Review of TCAS Events

FCOM Update
Following this event, the FCOM was revised to further clarify the
ADJUST VERTICAL SPEED, ADJUST RA:

Previous FCOM 1.34.80 page:

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New FCOM 1.34.80 page (March Revision):

TCAS - Recommendations

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Review of TCAS Events

Event N3

Aircraft 1: Was cleared to FL 370. Aircraft 2: Was also cleared to FL 370 by mistake. Controller discovered the mistake and instructed
Aircraft 2 to descend to FL 350.

Aircraft 1:
4Incorrectly
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interpreted the clearance which was not applicable to its aircraft 4Started to descend. 4TCAS issued a CLIMB, CLIMB RA. 4Did not follow the CLIMB, CLIMB RA, as it had visual acquisition of Aircraft 2.
TCAS - Recommendations
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Review of TCAS Events

Event N3

Aircraft 2:
4Received

a coordinated DESCEND, DESCEND RA 4Followed the RA 4Stopped descending, when it noticed that Aircraft 1 was also descending.

At the very last moment, Aircraft 1:

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Performed a sudden and violent escape maneuver, that resulted in injury to flight attendants and passengers.

TCAS - Recommendations

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Review of TCAS Events

Event N3
FL 370
CLIMB, CLIMB RA DESCEND, DESCEND RA

AIRCRAFT 2

Order incorrectly interpreted by AIRCRAFT 1

AIRCRAFT 1
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AIRCRAFT 2 Descend to FL 350.

AIRCRAFT 1 passes slightly below AIRCRAFT 2, with no lateral separation !!!

TCAS - Recommendations
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Review of TCAS Events

FCOM Update
For TCAS RA orders, the FCOM 3.04.34 was revised to delete the visual acquisition of the intruder line. Previous FCOM 3.04.34 page:

New FCOM 3.04.34 page (January Revision):

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For RA Alerts, the FCOM 3.02.34 and QRH TCAS

procedures were also revised by deleting the Attempt to see reported traffic line.
TCAS - Recommendations
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Review of TCAS Events

AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.

Previous FCOM 3.02.34 page

TCAS - Recommendations

New FCOM 3.02.34 page

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Review of TCAS Events

Additional information
ATC versus TCAS information:

ATC Radar:
4An

update rate of several seconds (from 4 to 10). 4Altitude data in 100-foot increments. 4Sudden vertical maneuvers are not immediately displayed.

TCAS:
4Interrogates
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all surrounded transponders every second. 4Mode S-equipped aircraft provide TCAS information in 25-foot increments.
TCAS Information is: - Updated 4 to 10 times faster - 4 times more accurate
TCAS - Recommendations
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Review of TCAS Events

Additional information
Visual acquisition limitations:

At high altitudes, it is difficult to assess:

4The

range 4The heading 4The relative height

At low altitudes, it is difficult to assess :

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4Whether

the aircraft is climbing or descending.

The traffic in contact MAY NOT BE the one that causes

the RA to trigger.

TCAS - Recommendations

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Review of TCAS Events

Conclusions

Other, more or less, serious events have occurred due to

the fact that the crew did not follow TCAS orders.

All such events emphasize the importance of the following:

- Always follow TCAS RA orders.
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- Do not try to visually acquire intruders, in case of RA orders.

TCAS - Recommendations

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Contents
Introduction TCAS Presentation Resolution Advisory Review of TCAS Events Recurrent TCAS Questions
AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.

Future TCAS Developments Conclusion

TCAS - Recommendations
Page 37

Recurrent TCAS Questions

Background

As of today, the following cases require TA mode selection:

4Engine

failure 4Dispatch with landing gear down 4Known nearby traffic, which is in visual contact 4Closely-spaced runways, converging runways, low terrain along the final approach

Recurring questions concerning TA mode selection:

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4Emergency

descent 4Engine failure 4Aircraft at its maximum ceiling altitude

TCAS - Recommendations

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Recurrent TCAS Questions

Emergency Descent

Most often due to rapid decompression. Performing an emergency descent in a busy airspace
increases the risk of generating traffic conflict.

A CLIMB, CLIMB RA order is not always requested:

4An
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ADJUST VERTICAL SPEED, ADJUST RA can be triggered (decrease the V/S).

TCAS - Recommendations

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 AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.

Recurrent TCAS Questions

Emergency Descent

TCAS - Recommendations
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Recurrent TCAS Questions

Emergency Descent

ADJUST VERTICAL SPEED, ADJUST

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DESCEND, DESCEND

TCAS - Recommendations

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Recurrent TCAS Questions

Emergency Descent

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In case of an emergency descent, Airbus does not recommend selecting TA mode.

TCAS - Recommendations

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Recurrent TCAS Questions

Engine Failure
In case one engine fails, the TCAS must be set to TA mode to comply
with AC 20-131:

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After an engine failure, aircraft performance is degraded. When TA is selected:

4Affected

aircraft not requested to perform an RA maneuver. 4No additional stress generated by a TCAS alarm in a stressful environment.
TCAS - Recommendations
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Recurrent TCAS Questions

Engine Failure

Airlines often complain that TA mode is sometimes too

restrictive, in particular for the A340-500/600, which is a:
4 Powerful aircraft
4

Fly-by-wire aircraft, not subject to stall in normal law.

For the following reasons, it is not recommended to

maintain TA/RA, in case of an engine failure:
4To
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have a common procedure for all aircraft 4If the intruder is TCAS-equipped: They will see that you are in TA mode. They will perform an RA maneuver.

TCAS - Recommendations

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Recurrent TCAS Questions

Engine Failure

In addition:
4The

ECAMs ENG SHUT DOWN Procedure requests the crew to select TA TCAS mode.

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4Airworthiness

Authorities have approved this TA mode selection, in case of an engine failure.

Airbus recommends the selection of TA mode, in case of an engine failure.

TCAS - Recommendations

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Recurrent TCAS Questions

Aircraft at its Maximum Ceiling Altitude

AC 20-131A defines the maneuvers that the

aircraft must be able to perform.

In particular, the aircraft must prove that it can

respond to a TCAS RA CLIMB order, even when it is at its maximum altitude.
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TCAS - Recommendations

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Recurrent TCAS Questions

Aircraft at its Maximum Ceiling Altitude
Speed (knots)

Time (s) V/S (feet/minute)

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Time (s)
TCAS - Recommendations
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Recurrent TCAS Questions

Aircraft at its Maximum Ceiling Altitude

These graphs show that the aircraft can follow:

4A

CLIMB, CLIMB TCAS RA order (1500 feet/minute) 4An INCREASE CLIMB, INCREASE CLIMB TCAS RA order (2500 feet/minute).

Always below VMO/MMO and above VLS:

4A330

aircraft, at 41000 feet, initial speed is M 0.82 (243 knots) The maximum weight is 177 tons. 4The Final Speed is 228 knots (Buffet Speed is 212 knots at 42000 feet)
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RA climb orders can be followed. Airbus does not recommend selecting TA mode, when the aircraft is at its maximum ceiling altitude.
TCAS - Recommendations
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Contents
Introduction TCAS Presentation Resolution Advisory Review of TCAS Events Recurrent TCAS Questions
AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.

Future TCAS Developments Conclusion

TCAS - Recommendations
Page 49

Future TCAS Developments

Background

Most vertical deviations for each aircraft (following a

TCAS RA order) are often greater than 300 feet.

Very large altitude changes often lead to conflict

with other aircraft in a busy airspace.

Due to excessive pilot reaction, uncomfortable

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load factors are reached.

TCAS - Recommendations

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Future TCAS Developments

Background

1000 feet

REAL PATH IDEAL PATH

0
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10
3500

20

30
3800

40

50
2000

60 seconds
5
-700

1
CLIMB, CLIMB

2
CLIMB, CLIMB

4
CLEAR OF CONFLICT
Page 51

MONITOR MONITOR VERTICAL SPEED VERTICAL SPEED

TCAS - Recommendations

Future TCAS Developments

Background

In addition, some operators have reported difficulty in

distinguishing the V/S needle, when it is red and in the red vertical speed sector (mainly on EIS1 screens).

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Improvements are anticipated in this area to help apply a TCAS RA order.

TCAS - Recommendations
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Future TCAS Developments

Planned Improvements

To facilitate QUICK RESPONSE to TCAS RA orders. To help AVOID OVERREACTION. To develop an awareness to maneuver only to the extent
necessary to avoid intruder aircraft.
Improvements are currently being reviewed and developed. Will provide pilots with pitch attitude information. For long range aircraft, improvement is anticipated for 2006.

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TCAS - Recommendations

Page 53

Contents
Introduction TCAS Presentation Resolution Advisory Review of TCAS Events Recurrent TCAS Questions
AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.

Future TCAS Developments Conclusion

TCAS - Recommendations
Page 54

Conclusion

4Even

if the number of TCAS alerts decreases, there are still missed mid-air collisions each year. Pilots must always follow TCAS RA orders.

4Some
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improvements are envisaged and are being developed to further assist pilots in effectively responding to TCAS warnings.

TCAS - Recommendations

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