AC
This has probably been posted before, and I’m sure you considered this, or similar events, when briefing Ministers that you knew exactly what occurred in ZD576, but to my non-pilot eyes this is bloody frightening.
The issues that stand out (to me) are highlighted toward the end. Notably, “complex”, “confusing”, “limited guidance” and, probably quite significantly, 2000’ AGL at the beginning of an incident that lasted 20 mins.
I also note the incident took place over 5 years after Mull, yet perfectly describes events reported by test pilots BEFORE Mull (but which were withheld from the BoI) and were STILL considered a safety hazard. One assumes in those 5 years the Mk2 had progressed from a development aircraft to one of acceptable design maturity (which it certainly wasn’t in June 1994) and the crew had the benefit of an acceptable number of hours experience (as opposed to a quick conversion course, followed by some months back in the Mk1, then having an immature and sub-airworthy Mk2 foisted on them a few days before the final flight).
AIR INCIDENT ODI/381/99 CREW REPORT
Chinook Mk2 ZD98l - 18 Squadron. RAF Odiham
5th October 1999, 15l0Z VMC I20kts, +6 deg C, 2000ft AGL
ZD981 was the Lead a/c of a 2 ship formation transiting from Shawbury to Odiham. Approx 10 mins after departing Shawbury, a small jolt was felt throughout the airframe and the capt'n in the RHS noticed that some of his fit instrument power flags briefly showed and the Master Caution Panel (MCP) lights flashed on and then off. A check of cockpit indications was made but all appeared normal.
Approx 2 mins later, similar symptoms were noted again without any subsequent indications of a problem. The jolts were very similar to that felt when the AFCS (Automatic Flight Control System) extendable links centre after a power interrupt and the conversation amongst the crew concentrated on this possibility.
Approx l min later, a series of jolts and power interrupts was experienced and the Captain elected to switch the AFCS off to prevent the a/c jolting.
Approx 2 sees later, the Master Cautions and all the captions on the CAP illuminated dimly. ALL power was lost to the primary flight instruments, including the main Al (Attitude Indicator) and the HSI (Horizontal Situation Indicator), and to the engine instruments. The only services remaining were those powered by the essential battery busbar. A loud hum was also heard through the intercom system which pulsed in phase with the captions of the CAP.
A check round the cockpit was made and all the CBs were checked and confirmed to be OK. The forward LCT (Longitudinal cyclic trim) was seen to be in the fully retracted position so speed was reduced to approx 80kts (Vmax with LCT retracted) as a precaution. The aft LCT indicated just below the ground position.
The Captain ordered all non essential equipment to be switched off and the formation was turned hack towards Shawbury - the nearest Military airfield. A practice Pan was in progress on guard so the formation changed frequency to Shawbury Approach and a PAN was declared.
CB's were checked once more and the crewman checked the TRU vents (Transformer Rectifier Unit) and the external bays for any evidence of a malfunction, but nothing untoward was seen.
The co-pilot attempted to find a relevant page in the FRC (Flight Reference Card) to assist with the diagnosis but none of the cards fitted the indications. The Captain had recently discussed electrical problems with the Brintel Simulator Staff and recalled a similar scenario where isolating the AC and DC cross-ties enabled one of the two electrical systems to be brought back on line. The co-pilot was ordered to trip the No 1 PDP (Power Distribution Panel) DC and AC cross-lies, but this had no effect and the CB was re-set.
The Captain then tripped the No.2 PDP DC then AC cross-ties. Tripping the AC cross-lie resulted in restoration of services from the No PDP. All the Captains flight instruments returned to normal as did the No2 ECU indications but all the services powered by the No.l PDP were still inoperative. The CAP partially cleared with the following captions remaining:
(a) L FUEL PRESS
(b) RECT 1
(c) AFCS 1&2
(d) XMSN OIL PRESS & XMSN AUX OIL PRESS
A check round the cockpit was done and the LCT indications were noted to be in the same positions as before.
With partial electrical power restored and the a/c in a safe configuration heading towards Shawbury, control was given to the co-pilot to enable the Captain to consult the FRC.
A scan of XMSN temps and pressures showed all to be normal, so the XMSN oil and AUX oil captions were dismissed as spurious. However the jump seat occupant wsa ordered to monitor the indications.
CAP indications were now similar to a single TRU failure with no cross-tie and Card 31 was used as reference. The Captain decided not to re-set his cross-tie CB having diagnosed a Bus-Tie fault of some kind.
The cross feed was selected open to start balancing fuel but with no success. The crewman operated the XFEED valves manually which cleared the L Pressure caption and Illuminated the XFEED caption.
An attempt was then made to program the forward and aft LCT in manual with no success indicated.
On short finals to land, the LCT were selected to retract for 30 secs IAW FRC35. At this point No2 a/c of the formation informed the Lead a/c that his aft wheels had swivelled through approx 45 degrees. The captain took control and made a vertical Landing followed by a gentle taxi forward to straighten the aft wheels. As weight was placed on the aft wheels a small power spike was seen on the Captains HIS power flag.
As the LCT were in an intermediate position it was decided to clear all the passengers from the a/c prior to shutdown. A visual inspection of the front and rear rotor disc attitudes appeared normal so the Captain elected to conduct a normal shutdown but with No2 PDP AC and DC cross-ties left tripped.
APU start was normal. The No.l generator was selected OFF with no change to indications. As No.2 generator was switched OFF thereby allowing the APU to come on line, all electrical services and indications returned to normal. The LCT were selected to AUTO and the fwd and aft LCTs were seen to trim to the GND position.
As a precaution against possible power spike induced FADEC faults, the ECL (engine condition lever) were selected to 55 degrees prior in ECU (electrical control unit) shutdown and the following codes were noted.
No1 DECU A7, Al, DB
No2 DECU 88
A normal shutdown was then completed with normal response from FADEC. Post shutdown it was noted that the avionics cooler fan had tripped.
This entire incident lasted 20 minutes. Indications were complex and confusing and initially the FRC were of limited guidance. In the end Cards 31, 32, 33 & 35 were consulted. It should he noted that the Brintel simulator training proved invaluable in producing a quick albeit partial solution to the loss of electrical power.
The fault was considered to be a major safety hazard, and had the crew been less experienced or in IMC or at night the outcome might have been considerably different!