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ASN Wikibase Occurrence # 153765
Last updated: 4 September 2019
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Date:17-FEB-2002
Time:22:25 LT
Type:Silhouette image of generic EC35 model; specific model in this crash may look slightly different
Eurocopter EC 135T1
Owner/operator:Bond Air Services opf Strathclyde Police
Registration: G-SPAU
C/n / msn: 0142
Fatalities:Fatalities: 0 / Occupants: 3
Other fatalities:0
Aircraft damage: Written off (damaged beyond repair)
Category:Accident
Location:near Muirkirk, East Ayrshire, Scotland -   United Kingdom
Phase: En route
Nature:Survey
Departure airport:Glasgow City Heliport (EGEG)
Destination airport:Glasgow City Heliport (EGEG)
Investigating agency: AAIB
Narrative:
While on task the helicopter then unexpectedly entered thick cloud. The police observer, occupying the front left seat, recalled that the airspeed indicator showed approximately 80 kt. The pilot, who was aware of the high ground on either side and reluctant to turn, decided that the safest option was to maintain his present track and descend using the radio altimeter as his height reference. When passing 1,000 feet agl, and still in cloud, the pilot selected the 'ALTITUDE' (ALT) and 'HEADING' (HDG) modes of the autopilot with the intention of maintaining his current altitude and heading. He then noticed that the helicopter had entered a turn to the right with approximately 15 angle of bank (AOB).

He manually overrode the autopilot and regained a westerly heading, but the helicopter re-commenced the turn to the right causing him to intervene once more. Following this second manual intervention the pilot recalled seeing discrete 'AP' and 'A.TRIM' red warnings and red 'P' and 'Y/R' annunciations. These warnings indicate that the autopilot has disconnected. The helicopter then entered a steep nose down attitude whilst turning to the right at about 45 AOB. The descent was rapid and despite his corrective control inputs the pilot was unable to prevent the helicopter striking the ground. The rear observer was seriously injured.

No defects were found with the helicopter or any of its systems, which could account for the behaviour of the helicopter and the loss of control. The approximate 'rate one' turn to the right on engagement of the 'HDG' mode was consistent with the correct operation of the autopilot turning the helicopter onto a selected heading to the right of its current heading. The uncommanded pitch down and 45 roll to the right, with the accompanying 'AP' and 'P','R' and 'Y' SAS warnings, was consistent with the pilot inadvertently pressing the 'AP/SAS DCPL' switch on the cyclic control, although he had no recollection of pressing this switch. This would have disconnected the analogue SAS and pitch damper, the associated pitch/roll EHAs and SEMAs and both yaw SEMAs, causing them to return to their null positions and thereby inducing unpredictable control inputs.

The decision to engage the 'ALT' and 'HDG' modes following inadvertent entry into IMC was however a reasonable one and would probably have been uneventful if the pilot had had a better appreciation of the autopilot system. At the time of the accident however he had received a level of training that exceeded that which was required and was
considered the norm for the industry.

The pilot was operating in weather conditions where it was possible that he would encounter cloud; a situation not unusual in police support operations. Because of the low ambient lighting conditions, and despite his best efforts to remain clear of the cloud, he was unable to see and avoid the cloud and entered IMC. Unlike pilots operating helicopters in support of Devon and Cornwall police operations in hilly areas with little cultural lighting he did not have the benefit of night vision goggles to improve his night vision and allow him to better see and avoid both terrain and cloud.

Despite being severely damaged in the impact, the structure of the helicopter had offered the occupants considerable protection from injury and it was clear that the more stringent crashworthiness design requirements of JAR 27 had therefore made a significant contribution to the crew's survival, in what might otherwise have been a fatal accident. Whilst the rear observer's seat had become detached from the floor, it could be established that the seat had remained attached to the floor during the initial impact and had subsequently become detached due to external loads caused by the seat contacting the ground as the helicopter slid on its right side and then rolled over. These loads would have far exceeded the loads for which the seat was designed.

Two safety recommendations were made on NVGs and autopilot training. Damage sustained to airframe: Per the AAIB report "Aircraft destroyed". As a result, the registration G-SPAU was cancelled by the CAA on 06-03-202 as "Permanently withdrawn from use"

Sources:

1. https://assets.publishing.service.gov.uk/media/5422fa2140f0b6134600081b/dft_avsafety_pdf_023427.pdf
2. https://siteapps.caa.co.uk/g-info/rk=SPAU
3. http://news.bbc.co.uk/2/hi/uk_news/scotland/1826661.stm
4. https://www.scotsman.com/news/three-hurt-as-police-helicopter-crash-lands-in-field-1-597663

Accident investigation:
cover
  
Investigating agency: AAIB
Status: Investigation completed
Duration:
Download report: Final report


Revision history:

Date/timeContributorUpdates
05-Mar-2013 06:55 TB Added
05-Mar-2013 07:24 TB Updated [Operator, Source]
05-Mar-2013 10:57 TB Updated [Time, Total occupants, Location, Phase, Nature, Source, Narrative]
05-Mar-2013 10:59 TB Updated [Source]
16-Feb-2015 15:43 Dr. John Smith Updated [Date, Departure airport, Source, Embed code, Narrative]
16-Feb-2015 15:44 Dr. John Smith Updated [Departure airport]
16-Feb-2015 15:45 Dr. John Smith Updated [Narrative]
24-Oct-2015 10:48 Aerossurance Updated [Time, Aircraft type, Operator, Destination airport, Source, Narrative]
24-Oct-2015 10:49 Aerossurance Updated [Narrative]
25-Oct-2015 11:45 Aerossurance Updated [Narrative]
07-May-2016 08:18 Aerossurance Updated [Aircraft type]
20-Jul-2016 14:25 Dr.John Smith Updated [Source, Narrative]

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