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10 Oct 2015 - The Portuguese AIB (GPIAA) have issued their final report into the 737-800, OK-TVT (39394 / 3899), operated by Travel Servis heavy landing accident at Terceira Azores (LPLA) in windshear which resulted in damage to the nose wheel bay and surrounding fuselage.

The Portuguese Civil Aviation Safety Investigation Authority (GPIAA) concluded their investigation in October 2015, establishing the following causes:

Causes:

  1. Procedural The flight crew did not comply with aircraft manufacturer procedures and company SOPs, which required a “go around” manoeuvre;
  2. Actuation The accident was due to an excessive control column forward input, causing aircraft negative pitch attitude which led to a very high impact loading on the nose undercarriage, leading to the severe damage of braces in the interior structure of the nose wheel bay, struts and fuselage frames. This followed a chain of events, which contributed to the accident including the wind gusts, turbulence, decision to fly above ILS G/P, the use of the A/T without A/P and the decision to land from an unstabilized final approach.

Contributing factors:

  1. The aircraft approach was conducted under turbulent conditions;
  2. The PF established an approach profile of one dot of scale above the nominal ILS G/S;
  3. The PF did not disconnect the A/T after disengagement of the A/P;
  4. Deviation from aircraft “stabilized approach” profile;
  5. The PM did not provide the required call outs for the “stabilized approach” deviations.
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Synopsis

The Boeing 737-800 aircraft, registration OK-TVT, with 6 crew and 164 passengers on board, operated a passenger “commercial air transport” (CAT) flight from Prague (Czech Republic), with a technical landing for refuelling at Terceira Azores island (LPLA). The flight ran smoothly (3450KM) until landing on runway 15 from Terceira Azores island (LPLA).

The commander reported that the visual approach to runway 15 seemed normal until the 5 NM from TD, even having found winds of about 50 kts intensity, and severe turbulence along the entire approach. Below 1000 feet began to find effects of "wind shear" with huge variations in intensity until the short final.

The aircraft made a hard landing on the wheels of the main landing gear, inflicting a maximum vertical load of 3.52 G and bouncing on the runway. The pilot did not discontinued the landing and the aircraft nose wheel hit the runway with a vertical acceleration of 2.75 G.

The inspection, performed by engineering services of the company revealed the existence of some folded braces in the interior structure of the nose wheel bay with some bent struts and cracks found in fuselage frames that had suffered structural damage from the vertical loads applied in the contact with the runway.

The aircraft had an initial repair service at Lajes airport, obtained a “permit to fly” and was authorized for a “ferry flight” to Prague for a “final repair” at TVS maintenance premises.

 

History of the Flight

The Boeing 737-800 aircraft, registration OK-TVT, with 6 crew and 164 passengers on board, operated a commercial passenger flight (Call sign TVS4130) from Prague (Czech Republic), with a technical landing for refuelling at Terceira Azores island (LPLA) and having the airport of Montego Bay (Jamaica) as final destination. Departed from the origin airport at 02:20 UTC, the flight ran smoothly (3450Km) until landing on runway 15 from Terceira Azores island at around 07:41 UTC, presented with partially cloudy sky, good visibility, surface wind was strong from southwest (190º/22kts gusting to 32kts), with direction variations between 160 ° and 230 ° and the air temperature 15 º C.

At the controls of the aircraft was the aircraft commander (PF), which had a great number of landings in that aircraft type at LPLA. The commander reported that the visual approach to runway 15 seemed normal until the 5 NM from TD, even having found winds of about 50 kts intensity, and severe turbulence along the entire approach. The commander reported that the visual approach to runway 15 seemed normal until the 5 NM from TD, even having found winds of about 50 kts intensity, and severe turbulence along the entire approach.

The aircraft developed a high rate of sinking, (sink rate) losing speed instantly which was counteracted by the PF with increasing power and attitude, in an attempt to stabilize the sinking. The aircraft made a hard landing on the wheels of the main landing gear, inflicting a maximum vertical load of 3.52 G and bouncing on the runway. The pilot did not discontinue the landing and the aircraft nose wheel hit the runway with a vertical acceleration of 2.75 G and an airspeed rounding 150 Kts. The PF was able to control the aircraft safely within the confines of the runway.

In a preliminary visual inspection sensed some deformation (creases / wavy corrugated) of the outer surface of the fuselage above nose wheel gear bay in both sides. Closer inspection, performed by engineering services of the company revealed the existence of some folded braces in the interior structure of the nose wheel bay with some bent struts and cracks found in fuselage frames that had suffered structural damage from the vertical loads applied in the contact with the runway. There were no injuries to persons.

 

Damage to Aircraft

The aircraft suffered a hard landing on RWY 15 at Lajes airport on the 22nd February 2014. After the landing, during a preliminary visual inspection, structural damages on the fuselage Section 41 were found - distortion of the fuselage skin and of the under structure around fuselage frame STA 294.5, lower lobe. (see pictures below). TVS deployed an engineering survey team to the site of the accident that performed the first damage assessment and Phase I “hard landing inspections” IAW AMM plus all possible Phase II inspections. All findings and deviations were reported to Boeing.

(Photos: GPIAA)

Operating Flight Crew

The flight crew was composed by two pilots: - the Commander as PF, and - the First-officer as PM.

The Commander, male, was 35 years old and detaining Spanish nationality. 6.819TT, inc 5.548 on type and 1.888 in command on type.

The Co-pilot, male, was 32 years old and detaining Czech nationality. 1.724TT

 

Meteorological Information

The METARs for the time of the accident were as follows:

LPLA 220800Z 20018G28KT 9999 VCSH FEW008 BKN011 15/14 Q1011=

LPLA 220700Z 19022G32KT 160V230 9999 FEW008 BKN012 14/13 Q1013=

In brief, the approach and landing at LPLA was conducted during the breaking-dawn with a cloudy sky, good visibility below 800 feet, recent light rain and variable gusting winds predicting moderate to severe turbulence.

 

Aerodrome Information

When the aircraft approached and landed at LPLA, it was in use the ILS approach procedure with landing on RWY 15, determined by the wind direction and velocity. The runway was wet and no physical deficiencies or other restrictions were reported, as per LPLA ATIS of 07:00 UTC

 

FDR Records Contents

The full report contains extensive FDM screenshots and FDR graphs. Much of the information is contained in this graphic. This shows a heavy first touchdown of 3.52G then a bouce and an increase in power. The nose is pitched down and a second touchdown of 2.75G occurs.

1 - The aircraft main landing gear, in the first touchdown, impacted the ground with a vertical acceleration of 3.52 G in a 3.9ᵒ pitch-up attitude (followed by a bounce of 15 ft differential pressure altitude)

2 - abrupt reduction of vertical acceleration to 0.21 G

Note: During above mentioned sequence, the control column has been slightly pulled up with corresponding deflection of the elevators, for an increase of 3.9ᵒ pitch-up attitude. With the bounce, the control column has been pushed down, actuating the elevators, and causing -1.9ᵒ pitch down attitude.

3 - The aircraft nose wheel impacted the RWY with 2.75 G vertical acceleration, due to -1.9ᵒ pitch down attitude and -663 ft/min rate of descent.

4 - Once again, the main landing gear touched the RWY at -588 ft/min rate of descent, sustaining 1.38 G vertical acceleration with 4.6ᵒ pitch-up attitude.

5 - Finally, a second smaller bounce of the aircraft occurred, showing 32 ft/min rate of climb, pitch attitude rising to 5.3ᵒ

6 - with a subsequent touchdown of -352 ft/min rate of descent and 1.16 G vertical acceleration.

 

Aircraft Approach and Landing

The GPIAA analysed that the captain disengaged the autopilot while descending through 1500 feet AGL but left autothrust engaged despite aircraft manufacturer and standard procedures' recommendation to also disconnect autothrust when the autopilot is being disengaged. The GPIAA annotated that the captain justified the decision to leave autothrust engaged with low speed protection due the turbulences prevailing. In addition, the captain decided to keep one dot above glide to have an additional safety margin in the severe turbulence encountered.

The GPIAA wrote: "When descending through “RA” 475 ft (07:41:09 UTC), the aircraft had a rate of descent of -1136 ft/min, thus abandoning the “stabilized approach” envelope, for about two seconds. At this stage would be advisable the flight crew to comply with the “go around” manoeuvre, as recommended by aircraft manufacturer and company SOPs. ... From 07:41:22 UTC (“RA” 168 ft) till 07:41:24 UTC (“RA 116 ft) the ILS G/S deviation augmented to 1.20 dot of scale DWN and further to 1.25 dot of scale DWN at 07:41:25 UTC (“RA” 93 ft) and 07:41:26 UTC (“RA” 71 ft) with a rate of descent attaining -1,040 ft/min. Due to G/S deviations more than one dot of scale, the aircraft abandoned again the “stabilized approach” envelope and the flight crew, for the second time, did not execute a “go-around”, as required by aircraft manufacturer and company SOPs. ... Between “RA” 169 ft (07:41:22 UTC) and “RA” 52 ft (07:41:27 UTC) the engine thrust has been reduced to “approach idle” with CAS within limits of “command speed”. This was a result of flying above the ILS G/S, and when the PF induced manually a -0.5ᵒ pitch down attitude the A/T maintained the engine thrust reduced to control CAS. In consequence, the rate of descent attained -1,184 ft/min (07:41:28 UTC), and once again the PF did not execute the “go around” manoeuvre. ... At this moment, missing three seconds for the aircraft to land the PF applied engine thrust and pulled the flight control column to increase the pitch-up attitude. Due to significant deviation from aircraft manufacturer recommended profile at threshold and flare heights, engine spool and late actuation of flight controls, the aircraft inertia didn’t allow in time, the avoidance of RWY impact with 3.52 G vertical acceleration. At the same time, when de-crabbing the aircraft with a right crosswind component, the landing occurred with a slight left bank instead of zero bank or right bank, as appropriate for the wind conditions. The manoeuvre was executed with insufficient input of aileron and rudder controls for the correct alignment of aircraft longitudinal axis with RWY centreline, which could have caused an extra aerodynamic drag. After the impact, the aircraft registered a bounce of 15 ft with 3.9ᵒ pitch-up attitude and the PF pushed forward the control column resulting in second impact of 2.75 G vertical acceleration with -1.9ᵒ pitch down attitude over the nose wheel causing a substantial damage in that area of the aircraft fuselage. The second bounce had a smaller amplitude resulting in aircraft attitude closer to manufacturer’s recommended touchdown profile and which was controlled by the PF."

 

The Portuguese Civil Aviation Safety Investigation Authority (GPIAA) concluded their investigation in October 2015, establishing the following causes:

Causes:

1. Procedural The flight crew did not comply with aircraft manufacturer procedures and company SOPs, which required a “go around” manoeuvre;

2. Actuation The accident was due to an excessive control column forward input, causing aircraft negative pitch attitude which led to a very high impact loading on the nose undercarriage, leading to the severe damage of braces in the interior structure of the nose wheel bay, struts and fuselage frames. This followed a chain of events, which contributed to the accident including the wind gusts, turbulence, decision to fly above ILS G/P, the use of the A/T without A/P and the decision to land from an unstabilized final approach.

 

Contributing factors:

1. The aircraft approach was conducted under turbulent conditions;

2. The PF established an approach profile of one dot of scale above the nominal ILS G/S;

3. The PF did not disconnect the A/T after disengagement of the A/P;

4. Deviation from aircraft “stabilized approach” profile;

5. The PM did not provide the required call outs for the “stabilized approach” deviations.

 

Safety Recommendations

These were all directed to Travel Servis and the Czchec Civil Aviation Authority

 

The full report is available for download here

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