Thai A359 at Frankfurt on Jan 1st 2020, about 800 feet AGL about 7nm from touch down

Last Update: August 10, 2022 / 19:04:41 GMT/Zulu time

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Photo of Thai Airways HS-THF, Airbus A350-900 — Thai Airways HS-THF, Airbus A350-900 (Photo credit: Alec BHX/KKC / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Jan 1, 2020

Classification
Incident

Airline
Thai Airways

Flight number
TG-926

Departure
Phuket, Thailand

Destination
Frankfurt/Main, Germany

Aircraft Registration
HS-THF

Aircraft Type
Airbus A350-900

ICAO Type Designator
A359

Airport
Frankfurt am Main International Airport, Frankfurt-am-Main

Airport ICAO Code
EDDF

A Thai Airways Airbus A350-900, registration HS-THF performing flight TG-926 from Phuket (Thailand) to Frankfurt/Main (Germany), was on final approach to Frankfurt's runway 07R when the aircraft descended to about 800 feet AGL (about 1150 feet MSL) before initiating a go around. The aircraft climbed to 5000 feet MSL, positioned for another approach and landed safely on runway 07R about 15 minutes later.

Germany's BFU reported following an unstable approach and low level flying the aircraft went around. The occurrence was rated a serious incident and is being investigated by the BFU.

On Mar 27th 2020 the BFU reported in their January bulletin, that the first officer (36, ATPL, about 4000 hours total, about 1500 hours on type) was pilot flying, the captain (43, ATPL, about 8000 hours total, about 400 hours on type) was pilot monitoring. Two more first officers (all with ATPL) were present on board. About 4 hours prior to landing a passenger had become ill, medical assistance had been requested to meet the aircraft upon arrival in Frankfurt.

Descending through 7600 feet towards Frankfurt approach (feeder) instructed the crew to increase the descent, to descend to 3000 feet, turn to heading 040 and cleared the flight for the ILS approach runway 07R Z, the crew was instructed to maintain 170 KIAS or more. The crew extended flaps to position 1 at about 6000 feet MSL, 18 seconds to position 2, the gear was lowered at 5100 feet, the sink rate was about 2000 feet per minute at that time. The aircraft intercepted the localizer and was following the LOC with increasing sink rate. The automatated call "two thousand five hundred" occurred, the autopilot was disengaged. The GPWS sounded 9 seconds later "Sink Rate" two times. 5 seconds later the automated call "one thousand" occurred and the GPWS sounded "Glideslope". 34 seconds after the 2500 feet call the pilot flying called a go around, the pilot monitoring informed Frankfurt Tower (which was the first radio contact with tower). At that point the aircraft was at 668 feet AGL/936 feet MSL 6.43nm before the runway threshold.

The aircraft performed a second approach, passed the point 6.43nm before the threshold at 2238 feet MSL and landed safely.

On Aug 10th 2022 the BFU released their final report concluding the probable causes of the serious incident were:

After a shortened final approach, the Airbus A350-941 was flying at night in good visual meteorological conditions unstabilized on instrument approach to runway 07R of Frankfurt/Main Airport. The glide slope of the instrument landing system was flown through from above. Starting at 3,300 ft AMSL, the flight path was continuously below the glisdesope. The cockpit crew aborted the instrument approach and initiated a goaround procedure about 6 NM ahead of the runway threshold 07R at 668 ft AGL, i.e. far below the glide slope.

The investigation determined:

- Errors in the programming of the waypoints in the flight management system
- Errors in the handling of the auto flight system for the approach
- Reduced situational awareness of the pilots in regard to the spatial position
- Communications and cooperation deficiencies within the flight crew.

The BFU annotated: "The BFU rated the PIC, the co-pilot and the two additional co-pilots as experienced due to their long aeronautical occupation and high total flying experience. "

The BFU analysed:

The co-pilot conducted the descent and final approach up until the go-around procedure.

The aircraft was flying behind another aircraft, during the descent and approach. Therefore, the flight crew assumed for their own flight path planning that they would start their approach to runway 07R after the preceding aircraft. The flight plan had been entered into the MCDU accordingly.

The controller informed them that due to the medical status the approach would be shortened and they would no longer land after the preceding aircraft. The controller instructed them to fly north toward the localizer of runway 07R. This reduced the remaining distance significantly. The CVR recording showed that the flight crew’s stress level increased. The PF’s orders were no longer clear and partially formulated as question.

The FCOM Chapter Initial Approach described that the flight plan had to be adjusted in the MCDU so that the vertical flight guidance could calculate the correct path and indicate it on the PFD. It was not possible to reconstruct the pilots input in the MCDU because the FDR is not designed to record these inputs.

A discussion of the pilots regarding a possible route discontinuity in the MCDU could not be heard on the CVR recording. Based on the chronological sequence of the aircraft configuration and the actual flight path, the BFU assumes that the flight plan had not been entered correctly into the MCDU. It is likely that the remaining distance above ground the flight crew had programmed in the MCDU was significantly longer than the actual one. It is very likely that the indication on the PFD of the calculated vertical flight path did not correspond with the mental image of the pilots.

Presumably, the flight crew had the impression to be much too high above the required flight path to approach the ILS glide slope of runway 07R. In this phase, the flying experience of the flight crew should have taken effect. Altitude, speed and the configuration have to be taken into consideration in order to estimate in which situation they are and then act accordingly. The BFU assess the situational awareness in this situation as insufficient.

Based on the FDR data it was possible to reconstruct that the PF controlled the descent with the Open Descent procedure. In order to increase the rate of descent, at constant high speed, the landing gear was extended and at times even the speed brakes and the flaps to increase drag. The flaps were also used to reduce speed. These were extended to their permissible operating limit. At the Flight Control Unit initially an altitude of 6,000 ft and then of 5,000 ft was selected.

The PF attempted to steer the aircraft in the HDG SEL Mode on to the localizer. Initially, the localizer was overshot toward the north.With heading entries the flight path was corrected towards east. The APPR Mode had not been activated, however, and therefore the LOC Capture Mode was not active. At about 1930:54 hrs, at 2,060 ft AMSL, the localizer was captured and the FMA indicated on the PFD LOC Captured. After the aircraft had captured the localizer of runway 07R with the mode Localizer Engaged, the mean rate of descent was about minus 2,000 ft/min and reached a maximum of minus 4,009 ft/min. The aircraft was flown with high speed at the permissible operating limit of flaps position 2.

The operator had stipulated in the OM-A, chapter Stabilized Criteria, that during approach below 1,000 ft a maximum rate of descent of minus 1,000 ft/min shall be flown. According to the Standard Callouts, the PM should inform the PF about deviations from certain parameters. On the CVR no such standard callouts could be heard, even though several significant deviations from such values existed.

During the final approach phase, the aircraft was not configured for landing, speed did not correspond with the landing configuration, the rate of descent was above the limit of 1,000 ft/min and the landing checklist had not been completed. Therefore, the approach was not stabilized in accordance with the OM-A requirements.

The PF disengaged the autopilot and initiated a go-around manoeuvre at 936 ft AMSL and 6.43 NM from the threshold of runway 07R.

The TAWS did not generate a Terrain Pull-up Warning, because the aircraft had not approached the ground far enough that it would have been triggered.

The flight crew could not explain to the BFU why they had flown so far below the glide slope. It was not possible for the BFU to draw any conclusions in regard to their intentions, from the interviews and the CVR recording.

The OM-A stipulated that two other co-pilots have to be present in the cockpit of the A350 fleet during take-off and landing. The pilots in their function as observers served as safety to recognise possible errors of the acting flight crew and intervene if necessary. Neither of the two pilots pointed out that the approach was too low.

Cockpit Communication

The recorded cockpit communication was mostly held in Thai. There were no briefings in regard to the approach route and the instrument approach. These were stipulated in FCOM PRO-NOR-SOP-160-160, 25 Apr 14.

The CVR analysis shows that during descent from cruise level a relaxed atmosphere prevailed in the cockpit. The first communications problem occurred on the radio frequency of the radar controller about four min prior to turning into the extended runway centre line. The radar controller asked about the ill passenger. This communication occurred outside the regular phraseology. The PM had problems to understand the content of the questions and asked the controller several times to repeat them. The CVR recording showed that the flight crew’s stress level increased continuously. This fact is proven by the instructions of the PF which were no longer clearly worded. The instructions for the PM were partially formulated as questions.

During the interview the BFU perceived that the PM could follow the conversation only to a limited extent. The BFU is of the opinion that the PM was not capable to follow the English questions.

Up until engine shut-off, the CVR recording did not contain any discussion of the flight crew in regard to the first approach occurring too low. After the first failed approach it would have been appropriate to carry out an error analysis.

Metars:
EDDF 012020Z 06004KT 9000 NSC M01/M02 Q1032 NOSIG=
EDDF 011950Z 06005KT CAVOK M01/M02 Q1032 NOSIG=
EDDF 011920Z 04004KT 360V070 CAVOK M00/M02 Q1033 NOSIG=
EDDF 011850Z 06006KT CAVOK M00/M02 Q1032 NOSIG=
EDDF 011820Z 06008KT CAVOK 01/M01 Q1032 NOSIG=
EDDF 011750Z 05008KT CAVOK 00/M02 Q1032 NOSIG=
EDDF 011720Z 07007KT CAVOK 00/M01 Q1032 NOSIG=
EDDF 011650Z 08005KT 040V100 CAVOK 01/M01 Q1032 NOSIG=
EDDF 011620Z 07003KT 030V100 CAVOK 01/M01 Q1032 NOSIG=
EDDF 011550Z 04003KT 010V070 CAVOK 02/M01 Q1032 NOSIG=
EDDF 011520Z 04004KT 010V070 CAVOK 03/M01 Q1032 NOSIG=