18-0542 ub en v04 pa

Bundesstelle fürFlugunfalluntersuchung German Federal Bureau of Aircraft Accident Investigation

Investigation Report Identification

Type of Occurrence: Serious Incident

Date: 11 May 2018

Location: Approach area Mönchengladbach Airfield

Aircraft 1: Motor plane

Manufacturer: Cirrus Design Corporation

Type: SR 22

Aircraft 2: Ultralight aircraft

Manufacturer: Remos

Type: GXNXT

Injuries to Persons: None

Damage: None

Other Damage: None

State File Number: BFU18-0542-GX

Abstract

In airspace E an airprox occurred involving a motor plane Cirrus Design Corporation

SR 22 flying in accordance with instrument flight rules and an ultralight Remos

GXNXT flying in accordance with visual flight rules. The closest lateral distance was

about 120 m at an altitude difference of about 25 ft.

Investigation Report BFU18-0542-GX

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Factual Information

History of the Flight

The motor plane was on approach to the Instrument Landing System (ILS) of

runway 13 of Mönchengladbach Airfield. One pilot and one passenger were on

board.

The ultralight was on VFR cruise flight from Grefrath-Niershorst to Aachen-

Merzbrück. Only the pilot was on board.

At 1535:21 hrs1, the motor plane pilot contacted Langen Radar: “[…] is in the descent

to 70 and routing GESBI.“ At 1537:23 hrs, the responsible controller issued an air

traffic control instruction to descend to 4,000 ft AMSL and at 1543:12 hrs, the

instruction to turn right to 015° and descend to 2,000 ft AMSL. At 1545:29 hrs, the

pilot received the air traffic control instruction to turn right to 050°. At 1545:59 hrs, the

controller issued the air traffic control instruction to turn right to 100° and follow the

ILS to runway 13.

At 1546:03 hrs, the Short Term Conflict Alert (STCA) generated an alarm (predicted

STCA) at the controller’s workstation. The radar targets in question at the controller’s

monitor become green and a warning signal sounds. At this time the distance

between the two airplanes was approximately 4.1 NM. At 1546:33 hrs, the alarm

changed from predicted to current. The colour of the targets changes from green to

red. At this time, the distance between the two airplanes was approximately 2.2 NM

and their vectors were converging.

At 1546:50 hrs (Fig. 1), the motor plane pilot received the first traffic information

regarding the ultralight from the controller: “[…] unknown VFR-traffic, twelve o‘clock,

one mile, moving left-right, two thousand five hundred feet. Do you have him in

sight?” The pilot answered: “Negative, […].“ At that time the two aircraft had a

distance of about 1.2 NM; their vectors were still converging. The motor plane was

still in descent and passed 2,800 ft AMSL. The ultralight was flying in 2,500 ft AMSL.

The controller stated that the moment he became aware of the impending conflict, he

had wanted to give the motor plane pilot traffic information. But he had to wait for the

radio transmission (clearance and acknowledgement by crew) of another aircraft.

According to the radio transcript, this lasted from 1546:35 hrs until 1546:50 hrs. At

1All times local, unless otherwise stated.


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the time, the STCA had already sounded for a while. But these alarms had been

related to other VFR traffic further north. At that time, they had not been relevant.

There had been additional STCA alarms regarding an airplane from Grefrath

dropping skydivers and other VFR targets. He also stated that in general one could

say that due to the numerous STCA alarms, especially in lower altitudes in airspace

E, it is difficult to separate the important from the irrelevant warnings. Especially

when workload is already high.

At 1546:58 hrs, the controller issued the second traffic information: “[…], traffic twelve

o’clock, half a mile, opposite, two thousand five hundred indicated, not confirmed.“ At

this time, the distance between the two airplanes was approximately 0.7 NM. The

motor plane was 200 ft above the ultralight and both aircraft were still on collision

course. At 1547:10 hrs, the two aircraft passed each other (Fig. 2). At 1547:16 hrs,

the motor plane pilot reported having the ultralight in sight: “[…] now have that aircraft

in sight, very close.“

Fig. 1: Depiction on the controller’s monitor at 1546:50 hrs

Source: Air navigation service provider, adaptation BFU

Remos GXNXT

2,500 ft AMSL Cirrus SR 22

2,800 ft AMSL

Descent (800 ft/min)

Aircraft uninvolved


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The motor plane pilot stated that he had been warned almost simultaneously by the

controller’s first traffic information and the on-board collision warning system. An

aircraft had been depicted at close distance, 100 ft, below his own flight altitude.

Since he could not see the other aircraft and the collision warning system depicted

the aircraft below his own altitude he had decided to deactivate the autopilot and

initiate climb.

The ultralight pilot stated that he had seen the motor plane for the first time when

they were passing each other. He had had the impression that it had come diagonal

from the aft right and had overflown him at close distance (about 30- 40 ft).

Subsequently, the Cirrus SR 22 landed at Mönchengladbach Airfield. The Remos

continued the flight to Aachen-Merzbrück.

Fig. 2: Radar image including flight paths: motor plane (red), ultralight (blue)

Source: Air navigation service provider, adaptation BFU

Closest distance

120 m horizontal /

25 ft vertical


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Personnel Information

Motor Plane Pilot

The 67-year-old pilot held a Private Pilot's License (PPL(A)) issued by the UK Civil

Aviation Authority on 24 May 2012 with the rating SEP (Land) and Night valid until

31 August 2018. In addition, he held a PPL(A) issued by the US Federal Aviation

Administration (FAA) issued on 16 March 2017 with the ratings SEP (land) and IR.

He had a class 2 medical certificate with the limitation VDL (Wear corrective lenses

and carry a spare set of spectacles) valid until 27 September 2019. He had a total

flying experience of more than 2,239 hours; of which 2,135 hours were flown as pilot

in command on type.

Ultralight Pilot

The 61-year-old pilot held a pilot’s licence for air sports equipment issued by the

Deutscher Aero Club e.V. (DAeC) on 9 August 2017 with no expiry date. The licence

listed the ratings for aerodynamically controlled ultralight aircraft and passenger

transport. He had a class LAPL medical certificate with the limitation VML (Correction

for defective distant, intermediate and near vision) valid until 24 November 2018. He

had a total flying experience of about 100 hours.

Air Navigation Service Personnel

The 30-year-old controller held an Air Traffic Controller's License issued by the

Bundesaufsichtsamt für Flugsicherung (BAF, Federal Supervisory Authority for Air

Navigation Services) valid until 27 January 2021.

Aircraft Information

Cirrus Design Corporation, SR 22

The motor plane involved is a four seater single engine low-wing airplane. The

aircraft was registered in the United States of America and privately operated. It was

equipped with the flight navigation equipment for instrument flights and in addition

with a traffic warning system (L3 Skywatch).


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Remos, GXNXT

The ultralight aircraft type involved is a two seater three-axis high-wing aircraft. It was

equipped with a transponder, which was activated. It was registered in Germany and

operated by a flying club which also chartered out the aircraft.

Meteorological Information

Mönchengladbach Airfield reported in the aviation routine weather report (METAR) of

1520 hrs the following weather conditions:

Surface wind 130° (080V220), 7 kt,

ground visibility of more than 10 km no significant clouds below 5,000 ft GND (CAVOK) Temperature: 18°C, dewpoint: 7°C

At the time of the occurrence the sun was in about 238° at 44° above the horizon.

Radio Communications

The motor plane pilot was in radio contact with the air traffic control unit Langen.

Radio communications were recorded. The transcript of the radio communications

covered the time span from 1535:21 hrs to 1547:40 hrs. The relevant content is part

of the chapter History of the Flight.

The Remos pilot was not in contact with Flight Information Service (FIS) Langen.

Airspace Information

The airprox occurred in airspace E. According to the Air Traffic Order, airspace E is a

controlled airspace in which IFR and VFR flights occur. VFR flights also receive

traffic information whenever possible. In addition, for VFR flights the following

weather conditions apply: 5 km flight visibility up to FL100); distance to clouds 1.5 km

horizontally and 1,000 ft vertically. Above 5,000 ft AMSL transponders are mandatory

for powered aircraft. According to Regulation (EU) No. 923/2012 air traffic control is

provided for IFR flights and these are being separated to other IFR flights but not to

VFR flights. All flights receive traffic information, whenever possible. Permanent radio

contact is required for IFR flights. All IFR flights require an air traffic control

clearance.


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Flight Recorders

The air navigation service provider provided the radar data recordings of the flight

paths for evaluation purposes.

On the basis of the recording the closest horizontal distance was determined as

120 m and 25 ft vertical.

Organisational and Management Information

Air Navigation Service Provider

The Manual of Operations Air Traffic Services (MO-ATS) regulates operation within

the air navigation service provider.

MOATS Chapter 212.1 lists the objectives of the air navigation services:

[…]

.11 prevent collisions between aircraft;

[…]

The air navigation personnel mainly has the following procedures available (MOATS

Encyclopaedia):

Air traffic control instruction

Directives issued by air traffic control for the purpose of requiring a pilot to take a

specific action.

Traffic information

Information issued by an air traffic service unit to alert a pilot to other known or

observed air traffic which may be in the proximity to the position or intended route of

flight and to help the pilot avoid a collision.

Traffic avoidance advice

Advice provided by an air traffic service unit specifying manoeuvres to assist a pilot

to avoid a collision.

The MOATS did not described under which circumstances traffic avoidance advice

for civil aircraft has to be issued. Only the heading Radar Flight Information Service

(RAFIS) concretised when traffic avoidance advice should be issued. The air


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navigation service provider provided this service for military aircraft under visual flight

rules.

513.3 Apart from the functions of the general flight information service, RAFIS shall

have the following additional functions: [...] traffic avoidance advice shall be issued if

the pilot does not have the reported traffic in sight; […]

The air traffic service provider is of the opinion that in airspace E the See and Avoid

principle has to be applied. One should refrain from issuing traffic avoidance advice,

because it is not always possible to predict the flight path of another aircraft and the

situation could become aggravated and one could not know if there is another aircraft

in the direction of the avoidance advice.

International Civil Aviation Organisation

The International Civil Aviation Organisation (ICAO) regulates in Appendix 11 the

tasks of the air traffic control service and of the flight information service. Air traffic

control service was defined as follows (Chapter 1): A service provided for the

purpose of […] preventing collisions […] between aircraft […]. Traffic avoidance

advice was defined as follows: Traffic avoidance advice. Advice provided by an air

traffic services unit specifying manoeuvres to assist a pilot to avoid a collision.

For airspace E the following was stipulated (Chapter 2.6):

IFR and VFR flights are permitted, IFR flights are provided with air traffic control

service and are separated from other IFR flights. All flights receive traffic information

as far as is practical. […]

ICAO Doc 4444 Procedures for Air Navigation Services – Air Traffic Management

listed the following:

8.8.2 Collision hazard information

8.8.2.1 When an identified controlled flight is observed to be on a conflicting path

with an unknown aircraft deemed to constitute a collision hazard, the pilot of the

controlled flight shall, whenever practicable: a) be informed of the unknown

aircraft, and if so requested by the controlled flight or if, in the opinion of the

controller, the situation warrants, a course of avoiding action should be

suggested; and b) be notified when the conflict no longer exists.


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European Union

Commission Implementing Regulation (EU) No 923/2012 defined under SERA.7001

the objectives of air traffic services. Among other things, it was stipulated that the

object of the service shall be to prevent collisions.

For airspace E the following was stipulated (SERA 6001):

[…]

(e) Class E. IFR and VFR flights are permitted. IFR flights are provided with air traffic

control service and are separated from other IFR flights. All flights receive traffic

information, as far as is practical. […]

The term traffic avoidance advice was defined in Article 2 as follows:

[…]

131. ‘traffic avoidance advice’ means an advice provided by an air traffic services unit

specifying manoeuvres to assist a pilot to avoid a collision.

[…]

Concerning collision avoidance, SERA.7002 documented the following:

Collision hazard information when ATS based on surveillance are provided.

(a)When an identified controlled flight is observed to be on a conflicting path with

an unknown aircraft, deemed to constitute a collision hazard, the pilot of the

controlled flight shall, whenever practicable:

(1)be informed of the unknown aircraft, and, if the pilot so requests, or if the

situation so warrants in the opinion of the controller, avoiding action shall be

suggested; and

(2)be notified when the conflict no longer exists.

Additional Information

Traffic Warning System L3 Skywatch

According to the manufacturer’s statements, this system warns against other aircraft

if they are equipped with a transponder which is engaged. It consisted of


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3 components (Fig. 3): a display, a Transmitter Receiver Computer (TRC), and a

directional antenna.

The directional antenna transmits omnidirectional Mode-C enquiries and receives

directional answers from aircraft in the vicinity equipped with transponders.

The TRC processes the signals the directional antenna received. These are indicated

on the display. In addition, acoustic warnings can be generated. The TRC can

process 30 targets at once but only indicates the 8 most important to ensure clarity.

On the display in the cockpit, the targets are indicated with distances and altitude

differences.

Fig. 3: Components, L3 Skywatch Source: SkywatchTM SKY497 Pilots Guide

Collision Warning System of Air Traffic Control

STCA warns the air navigation service personnel if the distance between two aircraft

is infringed (current alert) or will be in a predefined timespan (predicted alert). The

warning is indicated on the radar monitor and some systems also generate acoustic

warnings.


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Similar Occurrences

In 2013 and 2017 airproxes occurred which the BFU classified as Serious Incidents

and investigated.

One airprox occurred approximately 15 NM west of Mannheim involving an Embraer

Embraer EMB-505 on an IFR flight and a Cessna 177 RG on a VFR flight. The

closest lateral distance was 0.1 NM and the vertical 300 ft (BFU 7X001-13). The

Cirrus pilot was in radio contact with flight information service Langen.

Another airprox occurred on approach to Dusseldorf Airport involving an Airbus A320

on an IFR flight and an ultralight on a VFR flight. The ultralight pilot was not in

contact with any air traffic control unit. According to radar data, the closest vertical

distance was 100 ft and the lateral 0.8 NM. The Airbus flew over the ultralight with a

distance of 600 ft and a lateral of 0.07 NM (BFU 17- 1311-EX).

In both cases, as in the current one, no traffic avoidance advice was given, even

though radio contact with one of the flight crews involved existed.


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Analysis

General

All persons involved held the required licences and ratings.

The motor plane operated in accordance with IFR was in descent to the ILS

approach of runway 13 of Mönchengladbach Airfield (flight direction 100°). The

ultralight operated in accordance with VFR was flying with a heading of 225° at about

2,500 ft AMSL (level flight).

Individual Actions

Pilots

The motor plane pilot received traffic information from the air traffic control unit but

could not in time establish visual contact with the unknown air traffic. At the time of

visual contact, it was too late for an avoidance manoeuvre, because the two aircraft

were already passing each other. The pilot stated that the traffic warning system of

the Cirrus had indicated a target in close distance, 100 ft below. Since he could not

see it he decided to disengage the autopilot and initiate climb. He did not initiate a

lateral avoidance manoeuvre. The BFU is of the opinion that he could have asked air

navigation services for traffic avoidance advice. However, between the first traffic

information and the time both aircraft passed each other, only 20 s passed.

Therefore, realistically there was no time to ask for traffic avoidance advice, receive

it, and carry it out in time.

The ultralight pilot did not have any information regarding the approaching motor

plane. Since he was not on FIS frequency and had no collision avoidance warning

system on board he had to rely on the procedure See and Avoid. Especially on

collision courses this procedure has limits and without additional means it is

insufficient. By making use of the flight information service the pilot might have

received support in making a speedy and adequate decision. Due to the position of

the sun, it cannot be ruled out that the pilot was dazzled and could not see the motor

plane in time.


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Radar Controller

The controller had given the motor plane pilot the descent clearance to descend from

4,000 ft AMSL to 2,000 ft AMSL and the clearance to turn right to a heading of 100°.

This resulted in a collision course of the two aircraft.

The STCA began to warn at a distance of 4.1 NM between the two aircraft. After the

first alarm 47 s passed until the first traffic information. During that time the distance

between the two aircraft decreased to 1.2 NM and 200 ft.

Before the controller issued the first traffic information he issued an air traffic control

instruction to another aircraft which was not involved in this airprox. Already 32 s

prior to this instruction the STCA had generated an alarm. The BFU is of the opinion

that these actions had been given the wrong priority. Issuing traffic information as

collision prevention should have a higher priority as an air traffic control instruction,

given the real danger.

The controller issued 2 traffic information. The BFU is of the opinion that the first was

issued very late. Even though the pilot reported that he did not have any visual

contact, the controller did not intervene with the flight path of the motor plane. It

would have been possible to give the motor plane pilot an air traffic control instruction

for a lateral and/or vertical avoidance manoeuvre or issue traffic avoidance advice.

The BFU is of the opinion that it would have been necessary to issue a traffic

avoidance advice in order to prevent the airprox or the imminent collision. The BFU is

also of the opinion that in such situations just issuing traffic information is not

sufficient.

Defences

There were no indications of technical malfunctions of the STCA. Due to the

commonly high number of warnings concerning simultaneously existing conflicts and

the actual situation on the day of the occurrence, the controller’s attention was not in

time drawn to the impending near miss.

The air navigation service provider confirmed that they are still working on the

optimisation of the STCA.

The collision warning system of the motor plane supported the pilot in recognising the

oncoming unknown air traffic and therefore contributed to the prevention of the

collision. It could not prevent the airprox because the system was not able to issue

traffic avoidance advice.


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Organisational Influence

Traffic Information

The BFU had issued a Safety Recommendation in connection with the Serious

Incident near the omnidirectional radio beacon WALDA:

Safety Recommendation No. 01/2013

The air navigation service provider should amend their internal regulations for the

transmittance of traffic information and ensure that traffic information for danger

prevention can be transmitted to aircraft involved independent of airspace category

and flight rules.

Air navigation service personnel can issue traffic information only in time if they have

the option to view the situation in their assigned airspace at any time. The workload

made this at least more difficult for the controller. A timely traffic information and/or

traffic avoidance advice could have contributed to prevent the conflict.

Traffic Avoidance Advice

The argument of the air navigation service provider that issuing traffic avoidance

advice may result in an aggravation of the situation and therefore should not be given

is contrary to the specifications of EU (SERA.7002) and ICAO DOC 4444. EU, ICAO,

and the air navigation service provider define the object of air traffic control to prevent

collisions between aircraft. The BFU is of the opinion that issuing traffic information

alone is insufficient to prevent impending collisions.

The MOATS did not document an obligation to issue traffic avoidance advice for

collision prevention for civil air traffic. In order to provide the air navigation service

personnel with the necessary action safety such an instruction should be clearly

defined. The radar controller adhered to the regulations of the air navigation service

provider in force at the time.

The BFU is of the opinion that it should be ensured that all flights which are in radio

and radar contact receive not only traffic information but also traffic avoidance advice

or air traffic control instructions if this is necessary to prevent collisions.


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Conclusions

The causes of the Serious Incident were:

The motor plane pilot received an air traffic control instruction to descend

which crossed the altitude of the oncoming ultralight.

The controller’s reaction concerning the STCA warning was hesitant. The

prioritisation of the tasks was inadequate.

The instruction to descend was not cancelled and climb not instructed to

prevent the imminent airprox. A recommendation for a lateral avoidance

manoeuvre was also not issued.

The motor plane pilot received the first traffic information very late.

When the pilots had the other aircraft in sight it was too late to initiate an

avoidance manoeuvre.

Contributing Factors

The MOATS did not list any distinct instruction regarding the actions to be

taken by the air navigation service personnel to prevent collisions.

The ultralight pilot was not in radio contact with FIS and therefore had no

information regarding the imminent collision risk.


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Safety Recommendations

Recommendation No.: 01/2020

The air navigation service provider should adopt the specifications of the Secondary

Regulation (EU) No 923/2012 of the Commission of 26 September 2012

(SERA.700.2 – a) 1.) and the identical of ICAO (Doc 4444, PANS ATM 8.8.2.1. A))

regarding the issuance of traffic avoidance advice for collision prevention in their

Manual of Operations Air Traffic Services (MO-ATS) and give the air navigation

service personnel the action safety to take action for collision prevention.

Recommendation No.: 02/2020

The Federal Supervisory Authority for Air Navigation Services should ensure that the

stipulations of the Secondary Regulation (EU) No 923/2012 of the Commission of

26 September 2012 (SERA.700.2 – a) 1.) and the identical of ICAO (Doc 4444,

PANS ATM 8.8.2.1. A)) regarding the issuance of traffic avoidance advice for

collision prevention are taken into account in the Manual of Operations Air Traffic

Services (MO-ATS) and are implemented by procedural instructions.

Investigator in charge: Blanke

Braunschweig, 28 September 2020


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This investigation was conducted in accordance with the regulation (EU) No. 996/2010 of the European Parliament and of the Council of 20 October 2010 on the investigation and prevention of accidents and incidents in civil aviation and the Federal German Law relating to the investigation of accidents and incidents associated with the operation of civil aircraft (Flugunfall-Untersuchungs-Gesetz - FlUUG) of 26 August 1998. The sole objective of the investigation is to prevent future accidents and incidents. The investigation does not seek to ascertain blame or apportion legal liability for any claims that may arise. This document is a translation of the German Investigation Report. Although every effort was made for the translation to be accurate, in the event of any discrepancies the original German document is the authentic version.

Published by: Bundesstelle für Flugunfalluntersuchung Hermann-Blenk-Str. 16 38108 Braunschweig Phone +49 531 35 48 - 0 Fax +49 531 35 48 - 246 Mail [email protected] Internet www.bfu-web.de

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