West Atlantic B734 at Exeter on Jan 19th 2021, hard touchdown

Last Update: May 19, 2022 / 18:18:54 GMT/Zulu time

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Incident Facts

Date of incident
Jan 19, 2021

Classification
Accident

Flight number
NPT-05L

Aircraft Registration
G-JMCY

Aircraft Type
Boeing 737-400

ICAO Type Designator
B734

A West Atlantic Boeing 737-400 freighter, registration G-JMCY performing flight NPT-05L from East Midlands,EN to Exeter,EN (UK) with 2 crew, landed on Exeter's runway 26 at 02:34L (02:34Z) but suffered a very hard touch down. The aircraft rolled out without further incident. No injuries are being reported.

Locals report a post flight inspection found creases around the fuselage to the extent, that Royal Mail was unable to unload the mail.

On Jan 20th 2021 the AAIB announced: "A team of inspectors are continuing to gather evidence on site at Exeter Airport where they are investigating an incident involving a cargo aircraft which occurred yesterday, 19th January."

On May 19th 2022 the AAIB released their final report concluding the probable causes of the accident were:

The aircraft suffered a hard landing as a result of the approach being continued after it became unstable after the aircraft had past the point where the crew had declared the approach stable and continued. Despite high rates of descent being observed beyond the stable point, together with associated alerts the crew elected to continue to land. Had the approach been discontinued and a GA flown, even at a low height, while the aircraft may have touched down the damage sustained may have been lessened.

While the OM did not specifically state that an approach was to remain stable beyond the gate on the approach, the FCTM was specific that, if it did not remain stable, a GA should be initiated.

The commander may have given the co-pilot the benefit of doubt and believed she had the ability to correct an approach that became unstable in the final few hundred feet of the approach. However, had there been any doubt, a GA should be executed.

The AAIB analysed:

Conduct of the approach

Both pilots had previously operated into EXT and had no concerns about the ILS approach to Runway 26, despite it having a slightly steeper approach angle. The co-pilot had also conducted a FLAPS 40 landing at EMA, without event, on the previous sector.

During the cruise the crew calculated the landing performance and briefed for the approach. While they noted that there was a 3.5° GS they did not brief that they could increase the SINK RATE deviation call, for the ROD, from 1,000 ft/min to 1,150 ft/min.

The initial part of the ILS approach was flown appropriately, with the aircraft configured for the landing early and crew becoming visual with the runway at about 1,000 ft aal.

The criteria specified in the operator’s OM for an ILS approach to be stable were that the IAS should have been no more than 10 kt above VAPP and no slower than 5 kt below, a ROD of less than 1,150 ft/min (on a 3.5° glideslope) and within one dot of the GS and localiser. At 500 ft RA the aircraft was configured for landing, the IAS was VAPP +3 kt (143 kt), the ROD was about 860 ft/min and the aircraft was slightly above the GS. In terms of the criteria for a stabilised approach, the aircraft was stable at this point albeit close to the limit of the ROD. However, the ROD was increasing and soon after exceeded the stable approach maximum ROD of 1,150 ft/min. This was reduced to about 300 ft/min but soon increased again. At 320 ft RA the ROD had reached 1,700 ft/min, which was the greatest observed on the approach. While it was reduced again shortly thereafter, the ROD exceeded 1,150 ft/min on two more occasions prior to the landing and the recorded data indicated that 1,700 ft/min was nearly reached again at about 25 ft RA. These variations in the ROD had a corresponding effect on the aircraft’s position relative to the GS but while it came close to being one dot below the GS, at about 150 ft RA, it did not exceed it.

During these exceedances of the ROD the PM did not call “SINK RATE” as required by Section 2.1.17.5 of the OM. He did however, say “WATCH THAT SINK RATE”, at about 150 ft RA, after the second alert, when the ROD was 1,300 ft/min. The lack of a GA command may have given the PF the impression that the PM was content for the approach to be continued, despite three GPWS “SINK RATE” alerts being generated during the final 30 seconds of the approach. Additionally, while it may not have been explicit in the operator’s OM, that a GA should be executed if an approach does not remain stable, the FCTM stated ‘If the above criteria [stable approach criteria] cannot be established and maintained until approaching the flare, initiate a goaround.’

While the possibility of conducting a GA just before the landing was always in the commander’s mind, it was not considered by him as the aircraft “stopped flying” so quicky he felt it was too late to initiate one. He added that, in hindsight, a GA should have been initiated at that point, even though the aircraft would have more than likely touched down during the manoeuvre. While the aircraft may well have touched down during a late GA, this was a manoeuvre that was described in the FCTM and had been trained for during the pilots’ recurrent training.

The commander stated that the aircraft “stopped flying” just before it landed. This was probably a result of the reduction in thrust at about 100 ft RA. There was then an increase in thrust at about 30 ft RA. This was likely to have been an attempt to arrest the ROD of about 1,000 ft/min, just prior to the landing. Had the PF been more positive with her understanding of the situation and elected to GA, even if it was in the final few feet, the extent of the damage may have been reduced. If she felt she had become overwhelmed by the way the approach was progressing she could have handed control to the commander. He too could have taken control, as he recognised he probably should have, albeit in hindsight. The crew may also have been overloaded at the time to think a late GA was a realistic option.

The manufacturer’s approximate pitch attitude to maintain the GS was 1° nose up. During the final 500 ft the aircraft’s pitch attitude varied between 5° nose up and 6° nose down. While it is not unusual for changes to be made to the aircraft’s attitude to remain on a GS, such significant variations suggest there was either an element of over controlling or too great an adjustment to correct a deviation. This probably led to the divergences below the GS and excessive ROD leading to the GPWS alerts and subsequent hard landing. While the FD was on, its computed pitch and bank angles were not recorded on the FDR, but it should have provided appropriate guidance to the crew to allow a stable approach to be maintained.

The commander also stated that he felt it was too late for him to take control or call “go around” from about 100 ft RA. While the co-pilot was making adjustments to the aircraft’s path, throughout the approach as the wind reduced, SINK RATE alerts at 320 ft RA and 260 ft RA should have alerted them that the approach was not stable and a GA would have been an appropriate thing to do, despite there not being positive guidance in the OM as what to do after the aircraft has passed the stable gate at 500 ft.

The commander had confidence in the co-pilot’s ability and had flown with her on many occasions, it is possible this may have led to him to feel that the co-pilot was able to handle the situation and so did not call a GA or take control.

The operator commented that a B737 would use about 1,000 kg of fuel to fly a GA and another ILS approach. With 6,600 kg of fuel on board at the time of the accident, and 3,118 kg required to go back to EMA, there was enough fuel to fly a further three approaches before a decision to divert to EMA was needed to be taken. There was thus no fuel/time pressure to land off the first approach.

Operations Manual

The operator’s OM did not specifically state that an approach must remain stable from 500 ft RA (for a VMC approach) to touchdown, even though the FCTM did. Since the accident, the operator has amended the OM to clearly state that an approach ‘requires an immediate go-around’ if it becomes unstable after the stable point.

At the time of the accident OM Part B referenced the stable point in 2.1.14, ‘Stabilised Approach’, with regards to the TDZE. However, in Section 2.2.14.1, ‘Allocation of duties and standard calls’ it was refenced to 500 ft RA. Since the accident a note has been added to 2.2.14.1 to highlight that ‘approach stability requirements are with respect to TDZE, not Radio Altimeter height.’

Any change in IAS will need an adjustment to the aircraft’s pitch attitude to maintain the GS, which will also result in change to the aircraft’s ROD as shown in Figure 3. The manufacturer’s predicted aircraft attitude for a 3.5° GS was about 1° nose up. Given the wind was decreasing down the GS, the aircraft would not have maintained this attitude all the way to the flare, due to the changing conditions.

Pilot’s assessment

During one of the co-pilot’s previous licence proficiency checks it was noted that, during a single engine approach, the aircraft produced a “SINK RATE” alert on short finals. The training captain recorded this element as passed at second attempt and assessed her Flight Path Management as Baseline Minimum Standard. Since this event the operator recognised that there was no robust mechanism for tracking an individual pilot’s performance during a recurrent check and introduced a number of procedures to rectify this. While these new procedures may not have prevented the accident happening it should enable the operator to screen all of those pilots whose performance may be worthy of monitoring.

Manufacturer’s assessment of the airframe damage

As part of the original crashworthiness evaluation of the Boeing 737-400 passenger aircraft, the manufacturer considered a gear-down landing at high sink rate. They concluded that the wing box would remain intact after landing at the maximum permitted weight of 121,000 lb and a sink rate of 18 ft/second.

The manufacturer reviewed the recorded data for G-JMCY and assessed that the landing occurred with mass of approximately 116,700 lb and a sink rate of 24 ft/second. The wing box remained intact, preventing fuel leakage.

If the main landing gear shock absorbers bottom during a landing, the main landing gear beams act as a structural fuse for vertical loading. Correspondingly, the drag strut bolts act as a fuse for drag loading. The left main landing gear beam on G-JMCY was visibly distorted in an upward direction, but it remained intact, as did the drag strut bolts. The manufacturer assessed that this indicated that the landing did not reach the vertical or drag load limits.

Safety margins are lower in the aft fuselage skin, thereby accounting for the damage in this area. Overall, the manufacturer concluded that the damage sustained by G-JMCY was consistent with a hard landing.

Metars (no Metars were transmitted anymore past 02:20Z, but most of the METARs are missing for the previous days, too):
EGTE 190220Z 23010KT 9000 -RA SCT012 BKN040 12/10 Q1009=
EGTE 190150Z 23011KT 9999 -RA SCT012 BKN040 11/10 Q1010=
EGTE 190120Z 25011KT 9999 -RA SCT012 BKN040 11/10 Q1010=
EGTE 190050Z 21008KT 170V240 9999 SCT013 11/10 Q1010=
EGTE 190020Z 19008KT 9000 FEW015 SCT028 11/10 Q1010=
EGTE 182350Z 20009KT 170V230 9000 -RA FEW015 SCT028 11/10 Q1011=
EGTE 182320Z 18009KT 9000 -RA FEW010 SCT017 11/10 Q1011=
EGTE 182250Z 17009KT 9000 -RA FEW010 SCT017 11/10 Q1011=
EGTE 182220Z 19010KT 9999 FEW010 SCT015 11/10 Q1012=
Incident Facts

Date of incident
Jan 19, 2021

Classification
Accident

Flight number
NPT-05L

Aircraft Registration
G-JMCY

Aircraft Type
Boeing 737-400

ICAO Type Designator
B734

This article is published under license from Avherald.com. © of text by Avherald.com.
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