Denim Air DH8C at Barcelona on Oct 22nd 2009, landed without nose gear

Last Update: May 14, 2013 / 15:16:14 GMT/Zulu time

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Incident Facts

Date of incident
Oct 22, 2009

Classification
Accident

Aircraft Type
De Havilland Dash 8 (300)

ICAO Type Designator
DH8C

Spain's CIAIAC released their final report concluding the probable cause of the incident was:

The cause of the incident was the improper operation of the landing gear system by the crew that, due to both a lack of knowledge of said system and to deficiencies in the use of the available procedures, was unable to identify or correct the abnormal configuration of the Landing Gear Alternate Release Door.

The captain (38, ATPL, 6,300 hours total, 5,000 hours on type) was pilot flying, the first officer (34, ATPL, 2,060 hours total, 1,300 hours on type) was pilot monitoring. The aircraft departed Barcelona's runway 25L, the crew had selected the gear up and were climbing and accelerating the aircraft when they noticed about 3 minutes after departure that all three gear indications were red. The flight attendant was asked to visually confirm the status of the main gear and reported back, that both main gear legs were still down.

The crew stopped the climb at 7500 feet advising ATC they wanted to return due to gear problems. The aircraft was vectored for landing as number 2, while the crew used the alternate gear extension methode they noticed that gear alternate release door was open although its normal position was closed. The crew closed the release door which resulted in an alarming and deafening noise, so that they opened the door again. The alternate gear extension procedure was continued by selecting the gear lever down, which resulted in both main gear show green, the nose gear red, three amber lights because of open gear doors also illuminated. The crew declared emergency and advised the flight attendant who in turn informed the passengers. The approach was continued for a landing on runway 25R without nose gear about 21 minutes after departure.

The CIAIAC reported that about one hour after landing the nose of the aircraft was lifted with a crane, the alternate control in the cockpit for lowering the nose gear was actuated and the nose gear extended and locked properly. The CIAIAC stated: "The inhibit switch was found actuated in the cockpit and the overhead and floor doors were open. The PTU selector switch was in manual."

The alternate gear extension requires 8 steps to be taken:
1. actuate the inhibit switch at the alternate main gear extension handle to prevent the hydraulic (main) system supplying hydraulic pressure to retract the gear
2. select the (regular) gear handle down
3. open the landing gear alternate release door, which opens a bypass valve isolating the hydraulic lines to actuate the gear
4. Fully pull the alternate T-handle for the main gear (overhead panel), which will deploy the main landing gear struts
5. Open the Landing Gear Alternate Extension Door in the floor, which closes a valve to prevent pressurization of the auxiliary cylinder on each gear leg
6. Fully pull the T-handle for the nose gear (in the floor) to extend the nose gear
7. Use alternate indicating system to ensure all three struts are down and locked
8. If the main legs are pushed back by the wind and do not lock, use the manual hydraulic pump to lock the main gear

Tests by the CIAIAC revealed, that if a normal gear retraction is initiated with the overhead door open (but floor door closed) failed to retract the gear with all three gear indications indicating red. Closing the overhead door would initiate and complete the retraction of all gear resulting in a gear safe indication.

If a normal gear retraction is initiated with both overhead and floor doors open, the gear would not retract with all three legs indicating red. Closing the overhead door would retract the nose gear leg however leave both main gear legs down, the main gear indication would continue to show two reds, the nose gear indication would extinguish, the alternate gear indication would show green for both main gear legs for being down and locked.

In these two cases, upon closing the overhead door, the power transfer unit motor pressurizing the hydraulic system #2 from hydraulic system #1, would activate.

The CIAIAC analysed: "The “Landing Gear Alternate Release Door”, located in the overhead in the cockpit, was probably partially open when the crew reported to the airplane, but if so, this was not detected either by the CPT during her check of the cockpit or subsequently by either pilot at any time prior to takeoff. The airplane thus took off with this condition uncorrected." This resulted in all three gears legs not retracting upon the gear being selected up.

After the flight attendant had reported back that the main gear legs were still down, the flight crew opened the floor door to check whether the three alternate green lights were illuminated, the crew however - by the testimony - was unable to determine whether this was a test indication. The floor door was not closed again leaving the hydraulic bypass valve activated. The crew determined that all gear struts were down and locked, however decided to carry out the alternate gear extension. At that point it is probably the PTU switch was brought to manual thus engaging the PTU, however, as the pressures on #1 and #2 system were balanced the PTU would not start turning.

The crew started the alternate gear extension sequence looking for the inhibit switch, discovered that the overhead door was open and closed the door. This initiated the gear retraction prompting the PTU to start turning as well. The PTU thus created a deafening and alarming sound, the nose gear fully retracted, the nose gear doors closed again and the nose gear indication extinguished.

Due to the noise from the PTU the crew opened the overhead door again, which again activated the bypass valve. As the floor door had remained open, none of the auxiliary cylinders could move, the main gear therefore had not moved and actually remained in the locked position.

The CIAIAC analysed: "Had the crew not left the floor door open and had they not selected the PTU to manual, the landing gear would have fully retracted without making any abnormal noises. All of the gear lights would have gone out and they could have continued the flight." and continued: "At that time the aircraft was on final approach and had joined the airport’s traffic pattern. The crew was preparing for the imminent landing but without having prepared the aircraft in accordance with the emergency landing procedure with the nose gear up."

Neither the aircraft manufacturer nor the operator had considered in the procedures that the overhead door could prevent gear retraction. "In the event of an unsafe gear indication, the crew was instructed to perform other emergency procedures, including the alternate extension of the landing gear. Had a procedure been available to the crew that included a check of the position of this door, the crew could have quickly ascertained its abnormal position, corrected it and retracted the gear, allowing them to continue with the flight normally." Another operator however had identified the issue and adjusted their procedures to have the crew verify the overhead door before continuing with other procedures. The CIAIAC therefore recommended to de Havilland/Bombardier and the operator to adjust their procedures accordingly.

The CIAIAC further analysed: "The procedures were constantly interrupted by operational considerations, by ATC communications and by the attention required by the weather situation. The crew’s attention also drifted frequently due to emotional or secondary reasons, causing them to shift their focus away from the situation."

The PTU switch should not have been operated as no loss of hydraulic pressure in system #2 occurred. The CIAIAC analysed: "The crew’s reaction to the noise indicates a lack of knowledge of the system."

Had the crew shown more attention while reporting to the aircraft they would have detected the partially or fully open floor door and would have closed the door.

The CIAIAC continued the analysis: "Both pilots seemed to have insufficient knowledge of the alternate landing gear extension system, especially of the effect of the position of the “Landing Gear Alternate Release Door” and “Landing Gear Alternate Extension Door”. Moreover, due to the way noted earlier in which they performed the emergency procedures, and due to the cockpit conversations recorded, it follows that neither pilot had an in-depth knowledge of or familiarity with the QRH."

The CIAIAC went on analysing that the aircraft was carrying fuel for a round trip to San Sebastion and back, so that the crew would have had ample time to enter a hold and properly resolve the situation, the captain however repeatedly insisted to land as soon as possible. The CIAIAC went even more critical of the captain's performance analysing that the captain instead of sharing tasks in the cockpit began to read the checklists besides flying the aircraft, made decisions without listening to or taking consideration the advise by the first officer, the first officer on the other hand showed hesitation to speak up with clarity and insistence to get hear, the lack of demanding a go-around is "highy indicative of a failure to use this cockpit resource management technique". The CIAIAC thus stated: "Defective team management and the ineffective tasks sharing resulted in the poor oversight of the flight and of the airplane’s performance."

The CIAIAC analysed: "It is likely that the CPT was experiencing some kind of subtle incapacitation that could have affected her performance and that the FO did not detect it, despite having enough signs to warrant such suspicions." This analysis was contested by the Dutch Safety Board participating in the investigation representing the country of aircraft registration stating: "The Safety Board thinks that the matter of the so called 'subtile incapacitation' of the captain is speculative and not substantiated. The Board agrees with the CIAIAC that the captain did not act as might be expected but in the Board's opinion the behaviour could also be related to stress."

4 safety recommendations were released as result of the investigation.
Incident Facts

Date of incident
Oct 22, 2009

Classification
Accident

Aircraft Type
De Havilland Dash 8 (300)

ICAO Type Designator
DH8C

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