Happily the February loss of a Bond Helicopters EC225 Super Puma in the North Sea was non-fatal, and now it turns out that luckily it was in benign conditions for the survivors. That's because of three serious and unsuspected phenomena that led to the search operation being much more difficult than you'd imagine in the circumstances. The AAIB reports on them today.The helicopter, you may recall, descended fairly gently into the sea in darkness, visually observed by individuals on the rig to which it was heading. It floated and the 18 occupants quickly got into the liferafts. Between the aircraft, the liferafts and the individuals they had plenty of locator beacons. Nevertheless, it took a 27 minute search to find the survivors.
Here's why.
This is the problem as far as the AAIB can establish. First the
automatically deployable crash position indicator on the helicopter
failed to release and didn't transmit a signal. That aspect is still
under investigation and the AAIB doesn't venture a view as to how that
happened. It's obvious that in more serious circumstances that alone
could be a crucial issue.
But there's more. In the helicopter there were four locator beacons - known as personal locator beacons for individuals and emergency locator transmitters (PLB/ELT) on liferafts. One on each pilot's lifejacket and one on each liferaft - all of the same design.
They broadcast a signal on 406MHz to the Cospas/Sarsat satellite-based international SAR organisation, and they broadcast homing signals on the 243MHz and 121.5MHz international distress frequencies. You can also talk on the distress frequencies. But it's very important that the the telescopic antennas are extended and in the vertical position for maximum efficiency.
Cleverly, if they're close together then one of the beacons automatically becomes the master and the others stay in standby mode, partly to save battery power and partly to avoid confusing searchers.
But the passengers were also wearing wristwatch-type personal locator beacons which are legal and in routine use, but not formally certificated by the airworthiness authorities. Those, it now turns out, will also suppress the PLB/ELT signals. But their own signal is very much weaker - a theoretical 5 miles, but in practice less, compared to up to 40nm for the PLB/ELTs.
Furthermore, one of the four PLB/ELTs - mounted on one of the liferafts - did not activate and was not recovered. It's not known why it didn't activate.
And in any case it's emerged that the crew didn't actually know they had to correctly orient the beacons or that they even had extendable antennas.
The upshot was that despite there being three functioning ELT/PLBs in use, SAR aircraft did not receive any signal on 121.5MHz or 243MHz. And no voice signals were received either. In the end a faint 121.5MHz signal was detected, probably from a wristwatch beacon.
The AAIB, as you can read in the full report, wants CAA and EASA reviews of the whole sorry saga and some pretty rapid action on training.
Who'd have imagined.
But there's more. In the helicopter there were four locator beacons - known as personal locator beacons for individuals and emergency locator transmitters (PLB/ELT) on liferafts. One on each pilot's lifejacket and one on each liferaft - all of the same design.
They broadcast a signal on 406MHz to the Cospas/Sarsat satellite-based international SAR organisation, and they broadcast homing signals on the 243MHz and 121.5MHz international distress frequencies. You can also talk on the distress frequencies. But it's very important that the the telescopic antennas are extended and in the vertical position for maximum efficiency.
Cleverly, if they're close together then one of the beacons automatically becomes the master and the others stay in standby mode, partly to save battery power and partly to avoid confusing searchers.
But the passengers were also wearing wristwatch-type personal locator beacons which are legal and in routine use, but not formally certificated by the airworthiness authorities. Those, it now turns out, will also suppress the PLB/ELT signals. But their own signal is very much weaker - a theoretical 5 miles, but in practice less, compared to up to 40nm for the PLB/ELTs.
Furthermore, one of the four PLB/ELTs - mounted on one of the liferafts - did not activate and was not recovered. It's not known why it didn't activate.
And in any case it's emerged that the crew didn't actually know they had to correctly orient the beacons or that they even had extendable antennas.
The upshot was that despite there being three functioning ELT/PLBs in use, SAR aircraft did not receive any signal on 121.5MHz or 243MHz. And no voice signals were received either. In the end a faint 121.5MHz signal was detected, probably from a wristwatch beacon.
The AAIB, as you can read in the full report, wants CAA and EASA reviews of the whole sorry saga and some pretty rapid action on training.
Who'd have imagined.
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