Here is a list of all the Airworthiness Directives issued by DGCA India for the Civil variant of the ALH Dhruv (2008-to 2023). Source - DGCA website www.dgca.gov.in
Airworthiness Directive (AD). A regulatory document which identifies aeronautical products in which an unsafe condition exists, and where the unsafe condition is likely to exist or develop in other aeronautical products of the same type design. It prescribes mandatory corrective actions to be taken, or the conditions or limitations under which the aeronautical products may continue to be operated. The AD is the common form of mandatory continuing airworthiness information mentioned in Annex 8.
Source: ICAO Doc 9760 - Airworthiness Manual
(Thanks to Commander MK Singh for compiling this list. He has extensive flying in the Navy and Civil aviation. He is a crusader for safety in helicopter flight operations and part of the working group of the VAST under VAI)
1/7/08
1. AD 001- On one of the DHRUV helicopters, during inspection of IGB area, a crack was noticed. Since an unsafe condition has been identified that is likely to exist or develop on other aircraft of the same type design, this Airworthiness Directive is being issued for visual inspection and submit the compliance certificate to Certification and Airworthiness Group of RWR&DC, HAL, Bangalor
2. AD 002 - Crack was noticed at the bolt head of five bolt-blade fork (big) of two DHRUV helicopters.
3. AD 003 - Hydraulic System – 1 pressure and fluid loss was reported on one of the DHRUV helicopters. Likely cause of the leak was attributed to the rubbing of hydraulic hoses with LH TGB fairing.
4. AD -004 - On one of the DHRUV helicopter, there was an in flight warning for collective pitch anticipator (CPA) redundancy failure for engine-2. During check CPA connector was found to be loose. As a result of this, loss of CPA input to the FADEC has resulted and caused failure of CPA redundancy for engine-2.
5. AD 004 - On another DHRUV helicopter, there was a warning for CPA failure on both the FADEC when collective pitch was lowered after touch down. On investigation, it was observed that the CPA input to both FADEC was out of range. Further it was found that CPA moving end check nut was loose and tab washer used for locking the check nut was bent incorrectly. These factors had contributed to the CPA rigging disturbance and were the cause for the snag.
6. AD 004 - There was an in-flight power loss warning followed with large split in NG, TGT and torque parameters of the two engines. Investigations with diagnostic PC revealed that FADEC2 had logged CPA failure. On checking CPA circuit, one wire on the flying lead of CPA was found cut at about 4 inches from the connector due to sharp fold in the CPA flying lead.
2/3/09
7. AD 009 - Rotors Flight Control – Rotor Control – Marking on cyclic stick, trimming of L-angle of separator wall, provision of additional safety and modification of fork assembly.
1. To facilitate proper placement of rigging tool on cyclic stick during rigging, a marking on cyclic stick is provided.
2. Trimming of L-angle to clear interference with hydraulic tube bushes.
3. Added safety by introduction of split pin.
4. To increase clearance between FDR/CVR potentiometer as well as coll pick off fixed end and fork assembly by decreasing the lug width of fork assembly
8. AD 010 - Stabilizers – Vertical Stabilizer – Installation of web stiffener on front spar of fin torsion box assembly. To reinforce the front spar of fin torsion box assembly, as per board of inquiry recommendation.
9. AD 011 - During flight when HF transmission is on, amber light of tail rotor vibration warning system flickered. To rectify problem it was proposed by RWR&DC to replace the existing velocimeter Model No 7310 with velocimeter Model No. 8866-1 having improved EMI/EMC shielding.
16/02/10
10. AD 012R 1 - Rotor Drive (s) –Gearbox(es) – One time check for presence of water in MGB lubricating oil of Dhruv helicopter IDS assembly.
A case of water ingress into IDS assembly on one of Dhruv helicopter was noticed in 2006. Detailed investigation revealed that water ingress into Main Gear Box was through top cover (p/n: 201P620H 0000 207) of IDS. It was also observed that non-standard “O” ring was used, which resulted in improper sealing against water.
Usage of correct size “O” ring as per drawing was emphasised and as an improvement sealing of top cover using sealant was introduced as additional feature against water ingress.
A recent case of water ingress has come to notice on one of Dhruv helicopters. Preliminary investigation revealed existence of a connector on IDS inspection cover (p/n: 201P 636H 0006 201). This inspection cover, with connector on it, is not a standard part as per SOP. Further, the “O” ring of the top cover was found damaged. It is possible that IDS with such inspection cover and damaged “O” ring installed on top cover might have led to seepage of water into MGB of IDS.
The water presence in lube oil of IDS has very serious effects like corrosion.
11. AD 013R 1 - NAVIGATION – Dependent Position Determination – Design improvement in GPS antenna bracket.
1. On some of the Dhruv helicopters, incidents of GPS antenna along with bracket and connector breaking away from main structure during flights were reported.
2. Investigation by Failure Review Board attributed the failure of sheet metal antenna bracket to its inherent strength deficiency. Replacement of existing GPS antenna bracket with machined bracket was recommended.
3. Part breaking away from aircraft during flight may cause injury to person or damage property on ground.
12. AD 015R 1- TAIL ROTOR DRIVE – Gearboxes – Installation of modified parts of AGB assembly to control the interfacing tolerance for avoiding low lube oil pressure.
Controlling of the interfacing tolerance of AGB assembly (P/N 201P 655H 0000 001) parts to avoid internal leakage and to overcome low lube oil pressure of ALH AGB assembly.
01/04/10
13. AD 016 - Cracks were reported on two TRA flange assemblies.
HYDRAULIC POWER – Main – Additional inspections of tail rotor actuator (TRA) flange assembly for crack.
20/08/10
14. AD 017R 1 - Collective eye end of UCS connecting rod were found broken on two Dhruv helicopter after their forced landings
ROTOR (S) – Rotor heads(s) – One time check on connecting rod assemblies (UCS) for crack detection.
15. AD 018 - Crack was noticed at threaded area of bolt-blade fork (big) on DHRUV helicopter.
Rotor (S) – Rotor BLADES – One time fluorescent dye penetrant CD check on bolt blade fork (big) - MRB.
16. AD 019 - Free play of approximately 5 mm was observed on TRA assembly during 1000 hours inspection. Based on detailed inspection and study, vendor has identified that “PINs”p/n 3101-010 used on TRA p/n 3101-000 from serial number 40 to 145 are not heat treated to the drawing requirement. Existence of this condition significantly reduces the fatigue life and may lead to loss of directional control.
HYDRAULIC POWER – Main – One time check on tail rotor actuator
2/11/10
17. AD 020 - Crack was found during inspection on LH side of horizontal stabilizer mounting bracket fitted on vertical fin spar and IGB rib.
STABILIZER – Vertical stabilizer – One time check for crack on IGB rib on fin torsion box assembly & tail boom assembly AFT
09/06/11
18. AD 021 - Engine oil leakage was reported by pilot after last flight. On inspection, rear bearing lubricating oil pipe (return line) found damaged.
AIR CONDITIONING – Distribution – One time check on interference of air conditioning tube with engine oil scavenge pipe and modification for introducing improved clearanc
19. AD 022 - . In some of Dhruv helicopters cracks were observed in IGB rib bottom and associated area of fin torsion box assembly
STABILIZERS – Vertical Stabilizer – Reinforcement of IGB bottom rib and strengthening ofIGB rib in fin torsion box assembly.
04/07/11
20. AD 023 - During a sortie on one of the military Dhruv helicopter, at hover, prior to take off, low rotor warning was observed. Helicopter carried out a safe precautionary landing. On further investigation, it was noticed that the fixed eye‐end of the collective pitch anticipator (CPA), p/n 34LL03C502W3290 was detached from the body of CPA. Such failure may affect handling qualities of helicopter adversely.
Engine Controls – Power Control – Inspection of collective pitch anticipator.
02/09/11
21. AD 024 - In one of the civil Dhruv helicopter, it was observed that the elastomeric bush (p/n201P 636H 3000 201) was seating on the radius of TDS sleeve. This was due to the bearing flange assembly was done towards tail rotor side of TDS support bracket instead of towards FWD side of the helicopter. This wrong assembly may lead to gradual failure of the bearing leading to loss of tail drive power6
TAIL ROTOR DRIVE‐ Shafts – Check of elastomeric bush seating position on tail drive shaft assemblies (Seg.‐3 & Seg.‐4) in situ on the helicopter
27/02/12
22. AD 025 - The Alert Service Bulletin “One time torque check on mounting bolts of Main Rotor Blade” is issued on the basis of recommendation made in preliminary
investigation report on accident to BSF (Air Wing) Dhruv helicopte r VT-BSH (DW63) on 19-10-2011.
This AD, which prescribes/mandates action to be performed on to helicopters as stated above to restore an acceptable level of safety is hereby issued pursuant to CAR 21.3B. TC holder/ Operators are required to comply with the above stated AD within the
stipulated time.
23/07/12
23. AD 026 - During investigation of some of the incidents of Advanced Light Helicopter (Dhruv) owned by defense forces, it was found that the collective eye-ends of connecting rod assembly were broken.
Since an unsafe condition has been identified which is likely to develop on other Advanced Light Helicopters of similar type design,this Airworthiness Directive is being issued for installation of improved steel eye-ends in place of existing titanium eye-ends to achieve higher fatigue strength.
24. AD 027 - In one of the civil Dhruv Helicopter, step marks at spline area of input flange of Intermediate Gear Box (IGB) was reported.
25. AD 028 - In one of the Military Dhruv Helicopter, Pilot observed physical travel of collective lever obstructed at corresponding torque of 72 percent. Defect
investigation revealed that the clip assembly connecting FDR/CVR
potentiometer to control rod was found displaced by approximately 20mm upward from its designated position.
Introduction of split pins in FDR/CVR potentiometer attachments of cyclic and directional channels.
21/03/13
26. AD 030 - In accordance with the para 3.3 (v) of GM 21.91 of CAR 21, this
modification is considered as mandatory Major Modification by the TC holder as an unsafe condition has been identified which exists in other Advanced Light Helicopter (ALH)-Dhruv
This Airworthiness Directive is issued
i. To provide visual inspection means for opening and closing of pilot door , co-pilot door, sliding door and hinged doors; and
ii. To provide door opening and locking instructions on clamshell door.
02/12/14
27. AD 031 - During 500 hrs servicing if a civil variant Advanced Light Helicopter (ALH) Dhruv, it is observed that the cylindrical roller at the input side of IGB was overheated and damaged. This damge is attributable to Oil starvation. The type of failure is considered critical as it may affect drive line from MGB to TGB.
19/02/15
28. AD 032 - In one of the ALH dent mark was observed on end plate RH side. Aldo dent and erosion on protection strip delamination was observed on TRB. It was found that one screw from TGB fairing RHS-Attachment came out and hit the TRB first then got embedded into plate. This type of failure is considered critical and it may affect both TRB & End Plate.
17/10/16
29. AD 034 - During 500 inspection change in CT density was observed on collar region of some of the main rotor blades of Dhruv helicopters. This indicates onset of local delamination.
01/06/17
30. AD 035 - In one of the ALH restrictions of movement was observed in the longitudinal circuit on Main Rotor Actuator(MRA) and Tail Rotor Actuator (TRA). Restriction on movement of circuit would lead to reduced controllability of helicopter. This type of failure is considered critical and it may affect controllability of helucopter.
19-10-2011
31. AD 036. Multiple occurrences of abnormal sound/possible surge and power loss of TM333-2B2 engines installed on ALH Dhruv Civil Helicopters along with vibration and jerks in cockpit during flight.
02/02/21
32. AD 037 - On one of the Military(IAF) helicopter during flight, Hydraulic System-1 Low level warning light came on and helicopter made precautionary landing. On further inspection Crack was observed on the valve body lug of Main Rotor collective Actuator of system-2 and failure of the lug resulted in the leakage of the hydraulic oil from O-Ring interface
13/07/23
33. AD 039 - During a routine sortie, Indian Navy ALH MK-III helicopter ditched into water close to Mumbai coast on 08/03/23 where in control loss in the collective channel was noticed during the flight. Post incident inspection control rod body in the collective control circuit was found broken.
My comments on this exhaustive list of ADs.
1. So many refer to the CPA (Collective Pitch Anticipator) -far too many. The problem is listed from 2008 and caused due to incorrect wiring, bad quality of the CPA bracket and so on. Clearly a workmanship issue. Really!!! Does it take so many incidents for HAL to realise there is a problem? My helicopter suffered this failure in 2004, the AD is issued in 2008. It means that there must have been countless more failures in between!
2. Water ingress into the MGB relates to use of the incorrect 'O' ring. This is only replaced at the OEM, so the operator had no hand in this. Again, it is the quality of workmanship at HAL. Water ingress into the sealed MGB is really really bad news.
3. Instances of the collective eye-end failures. Again a clear sign of vibration being the culprit.
4. ...identified that “PINs”p/n 3101-010 used on TRA p/n 3101-000 from serial number 40 to 145 are not heat treated to the drawing requirement. This means that unsafe items have been installed at HAL during production.
5. The AD AD 013R 1 is issued in 2010 and mentions that the GPS antenna bracket flew off. This had happened to a Naval helicopter in 2007, so it looks like HAL waited till 2010 before informing the DGCA only when a Civil helicopter lost its GPS antenna.
6. Rubbing of hydraulic pipelines is again a clear case of bad workmanship at HAL. We had so many pipelines rubbing and wearing out, but more of this later.
The CPA is the Collective Pitch Anticipator. Whenever there is an increase in power demand by moving the collective lever up, the engine rpm tends to lag because the fuel pump governor takes time to sense the transient droop in the turbine rpm before feeding more fuel to the engine.
All FADEC engines (like the ALH) use an electronic means of providing an advance information of the position of the collective pitch lever to the engine. This way, the engine already knows the collective is going up and provides more fuel at a faster rate when increasing the collective. So the CPA is something like the ‘coarse’ control for fuel, and the stepper motor / N2 sensing does the fine tuning. The opposite happens when reducing the collective and an rpm overshoot is prevented. Mi8 pilots will identify very well with this phenomenon, without a FADEC and the CPA.
In case the CPA stops sending signals to the engine(s) then an increase in collective will cause the N2 and Rotor RPM to droop, giving a “Rotor Low” audio. This is what happened to me, luckily we were on ground. Imaging this happening to both engines in the air – wild swings of the rotor rpm, and the pilot just won’t know what hit him. The reason? A very badly made bracket where the CPA is attached to the airframe, or shoddy wiring.
No comments:
Post a Comment