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ASN Wikibase Occurrence # 44117
Last updated: 3 September 2019
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Date:30-MAY-2006
Time:16:45
Type:Silhouette image of generic EC35 model; specific model in this crash may look slightly different
Eurocopter EC 135P1
Owner/operator:MedStar
Registration: N601FH
C/n / msn: 0069
Fatalities:Fatalities: 1 / Occupants: 4
Aircraft damage: Written off (damaged beyond repair)
Category:Accident
Location:Washington, DC -   United States of America
Phase: Approach
Nature:Ambulance
Departure airport:Washington, DC
Destination airport:Washington, DC (DC08)
Investigating agency: NTSB
Narrative:
The pilot reported that, during his first approach to the hospital helipad, the helicopter "shuffled," and the No. 1 engine rpm increased. The pilot stated that he increased collective pitch, reduced the throttle on the No. 1 engine, and aborted the landing. He noted that the No. 1 engine was no longer controlled by the full authority digital engine control (FADEC) system and that he had to control it manually. The pilot twice overflew the helipad, and, while maneuvering for another approach, he lost control of the helicopter, and it descended and struck a tree and the ground. Examination of the throttles, throttle linkages, engines, control systems, cockpit display system (CDS), and FADEC units revealed no evidence of any preimpact mechanical anomalies.

Postaccident testing of the engines and analysis of data retrieved from the CDS and FADEC units revealed that the accident pilot had inadvertently moved the No. 1 throttle out of its neutral detent, placing the engine in manual mode and out of FADEC control. Although the pilot recognized that the No. 1 engine was no longer controlled by the FADEC, he responded with further manual throttle adjustments and did not perform the published procedure to restore FADEC control to the engine. The data showed that, as the pilot continued to manually control the No. 1 engine, he subsequently moved the No. 2 throttle out of its detent, placing that engine also in manual mode and out of FADEC control. With neither engine under FADEC control, the pilot attempted control of the rotor rpm while controlling both engines manually. This configuration resulted in a high-workload scenario in which it would be particularly challenging for the pilot to control the helicopter during the maneuvering and approach-to-land phases of flight.

The accident helicopter was the only EC-135P1 CDS variant in the operator's fleet. Its engines, its displays, and its procedure for restoring FADEC control differed from the EC-135 variant in which the accident pilot was trained. According to the manufacturer's training guidelines, differences training is recommended before a pilot who is trained on another variant flies the EC-135P1 CDS. However, the investigation revealed that the operator provided the accident pilot only about an hour of formal differences training in the EC-135P1 CDS, and there was no evidence that the training adequately covered that variant's FADEC-restore procedures and other issues pertinent to flight safety. The pilot had accumulated about 914 hours of flight experience in EC-135s, with about 45 hours in the EC-135P1 CDS variant.

The accident was not the first indication to the operator that pilots who were trained in another variant experienced difficulties with the accident helicopter. According to one other pilot and the accident pilot, they each previously experienced events involving loss of FADEC control in the accident helicopter (in November 2005 and March 2006, respectively) but completed successful landings. The operator determined no mechanical explanation for the events and did not report, and was not required to report, them to its Federal Aviation Administration (FAA) principal operations and maintenance inspectors. The other pilot reported that, at the time of his November 2005 event, he was untrained in the EC-135P1 CDS and was completely unfamiliar with the procedure required to restore FADEC control. That pilot reported that, during his event, he oversped the helicopter's engines and the main rotor, and, as a result, the operator removed the helicopter from service, conducted inspections of the engines and main rotor system, and determined that differences training was needed for the EC-135P1 CDS; however, the operator failed to adequately provide such training. Because the FAA had no knowledge of the previous events with the accident helicopter, it had no indication to suspect that the differences training implemented by the operator was deficient.

Probable Cause: The operator's inadequate training program and the pilot's failure to maintain control of the helicopter following his inadvertent disabling of the No. 1 and then the No. 2 engine full authority digital engine control system.

Sources:

NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20060607X00691&key=1


Revision history:

Date/timeContributorUpdates
28-Oct-2008 00:45 ASN archive Added
18-Aug-2010 15:17 TB Updated [Aircraft type, Other fatalities, Narrative]
05-Mar-2013 06:58 TB Updated [Phase, Nature, Source, Narrative]
05-Mar-2013 10:02 TB Updated [Aircraft type]
07-May-2016 10:57 Aerossurance Updated [Time, Aircraft type, Source, Narrative]
21-Dec-2016 19:24 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
05-Dec-2017 09:11 ASN Update Bot Updated [Other fatalities, Source, Narrative]

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