UFCM
short&shapeless
Not a complete answer to your questions, but the following are references which are, or were, in the public domain:
House of Lords debates
Monday, 5 March 2001
The honourable Member for Tatton, in a debate in the other place on 27th June, reported that according to the Ministry of Defence there were 6 UFCMs involving Chinooks in 1994, five in 1995, six in 1996, five in 1997, seven in 1998 and six in 1999. That is 35 incidents in all, in six of which the cause was never found.
(This list is available in detail somewhere, but I cannot locate it at the moment - TheAerosco)
Written answers
Tuesday, 30 October 2001
The table lists the incidents of uncommanded flying control movements in Chinook helicopters since 1 January 1999 and their determined causes.
Uncommanded flying control movements in Chinook aircraft since 1999
Date Tail number Cause
1999
12 March ZA712 Faulty AFCS
17 March ZA718 Faulty DASH actuator and directional gyro
20 April ZD983 Directional gyro out of tolerance
29 April ZH775 Faulty AFCS and directional gyro
14 June ZA718 Faulty directional gyro
29 July ZA718 Faulty AFCS and directional gyro
29 October ZA711 Faulty directional gyro
18 November ZA711 Faulty directional gyro
2000
6 January ZA714 Faulty AFCS
6 January ZA718 Faulty AFCS
11 February ZA682 Faulty vertical gyro
4 April ZA682 Faulty DASH actuator gear assembly
5 April ZA679 Faulty DASH actuator
5 April ZA684 Faulty directional gyro connector
30 May ZA710 Faulty AFCS
24 July ZA679 Faulty AFCS and DASH actuator
5 August ZA674 Faulty cables to AFCS
9 November ZA671 Faulty vertical gyro
12 November ZA671 Faulty AFCS
2001
17 January ZH777 Units replaced following pitch oscillations
1 March ZA709 Faulty directional gyro
1 May ZA674 Faulty directional gyro
24 May ZA680 Faulty lower control actuators
5 July ZD981 Faulty attitude indicator
Extract from US Army "Flightfax" December 1998
A look at the issues
Uncommanded flight-control inputs
The May 1998 issue of Flightfax contained the
first-person accounts of the crew of a CH-47 that did a barrel roll. As a result of that
incident, Aviation Safety Action Message CH-47-98-ASAM-01 (151327Z Oct 98) requested
information from users on uncommanded control inputs. Input from users confirmed
that this was not the only incident of uncommanded flight-control input experienced
in the CH-47 community in the last several years.
According to the Analytical Investigation Branch
at Corpus Christi Army Depot, 21 activities
responded to the ASAM, reporting 27 AFCS/electrical malfunctions,
4 hydraulic-related malfunctions,
4 unknown causes,
and 3 suspected ice-and-water contamination incidents.
Following are some examples.
1. While in cruise flight at 10,000 feet msl and 126
KIAS, the aircraft experienced an uncommanded pitch
down of 20 to 25 degrees. When the PC applied aft
cyclic, the aircraft pitched up then down before the
PC regained control. The aircraft lost 500 to 1,000
feet of altitude during the sequence. When there
were no additional problems, the crew elected to
continue flight to their destination; they flew another
2 hours without further incident. It was later
determined that the incident was caused by failure of
the pitch axis portion of the AFCS. It is suspected
that, during the sequence, excessive control inputs
led to excessive flapping and lead-lag,
resulting in failure of the
shock-absorber mounts.
2. During flight-control check, the crew
experienced control binding, with the cyclic limited
to 4 inches forward movement and 1.5 inches lateral
movement. The crew chief stated that the forward
head was moving while the aft head was stationary.
Pressure was in normal ranges, and the problem
persisted for 5 minutes. The situation could not be
duplicated by maintenance, but an actuator problem
was suspected.
Update
Last year, a CH-47 miraculously returned to a
wheels-down attitude at 250 feet agl after rolling
360 degrees in flight. The Army Safety Center, the
CCAD Investigative Analysis Unit, AMCOM, and
Boeing continue to monitor and evaluate all CH-47
flight-control anomalies to determine the cause of
the incident. Following is a recap of ongoing actions:
1. AMCOM’s Systems Engineering Department
and CH-47 PEO/PM are currently preparing an ASAM
that addresses findings, recommendations, and
corrective actions developed to date.
2. A dehydrator will be issued in the near future
to remove contaminants from flight hydraulic
systems.
3. All chrome-plated aluminum end caps on
servo-cylinders will be removed and replaced with
chrome-plated stainless-steel end caps.
4. Several operational controls will be
implemented to enhance early detection of flight-
control lockup.
5. By-the-book maintenance is being emphasized.
For example, mechanics must ensure that all
hydraulic lines or components are capped and
plugged as soon they are disconnected; all
previously used or leftover hydraulic containers
must be disposed of; and all hydraulic components
received from the supply system must be drained
properly.
—MSG Ruben Burgos, Aviation Systems & Investigation Division,
DSN 558-3703 (334-255-3703),
Extract from US Army "Flightfax" October 2000
Uncommanded flight-control inputs:
This is an ongoing issue within the
community that has yet to be resolved. Investigations have
been conducted, but none have turned up conclusive evidence
of the cause of any of the reported incidents. ASAM
CH-47-97-ASAM-01 (151327Z Oct 97) and CH-47-99-ASAM-02
(161228Z Feb 99) have been issued to address suspected
causes, and to ensure the proper operation of the aircraft
systems. Units should comply with the published
messages, and conduct all maintenance procedures by
the book. If any flight control anomalies are experienced they
should be documented thoroughly and reported
through unit safety and maintenance channels.
Hydraulic System purification:
Historically the CH-47 flight control systems
have never been serviced or the filters changed unless there
was a maintenance problem requiring action. The fact that
the systems were never serviced was highlighted during
the investigations that tried to determine the cause of the
uncommanded flight-control inputs reported from the field.
CH-47-99-ASAM-02 (161228Z Feb 99) requires the
purification of all aircraft flight and utility systems, and
CH-47-00-ASAM-03 (012043Z Jun 00) details the sampling
and reporting procedures. This purification and reporting is
designed to: remove contaminantes (water,
particulates, air, solvents), improve system performance,
extend fluid life, and establish a baseline for future
investigations.