Underwater Locator Beacon (ULB) is a device fitted with CVR or FDR as well as to aircraft fuselage, which is used to locate the crash spot if an aircraft crashes into waterbody.
What is ULB?
ULB's are pinger systems which are designed to activate upon water crash, so that search and rescue team could spot the wreckage immediately.ULB's are triggered by water immersion (salt and fresh water), which then will emit ultrasonic pulses (pinger signals)at specific intervals on a frequency of 37.5 kHz (+/- 1 kHz), for a period of atleast 30 days and has a detection range of 1-2Kms. But the ULB's attached to airframe are generally Low Frequency ULB's which emits pinger signals at a frequency of 8.8 kHz for a longer period of 90 days. They are designed in such a way that they can survive the accident and can fucntion properly afterwards as well. Research carried out by the French Bureau d'Enquêtes et d'Analyses (BEA) published in 2011 showed that they have had a 90% survival rate spanning 27 air accidents over the sea.
Updated European aviation safety regulations on air operations require that the transmission time of the ULB, attached to the flight recorders, be extended from 30 days to 90 days by 1 January 2020 at the latest. The same rules also require that by 1 January 2019, most large aeroplanes operated over routes that go farther than 180 NM from a shore are equipped with an additional airframe low frequency (8.8 KHz) ULB. Low-frequency ULBs are required to be compliant with ETSO-C200 or equivalent and they should not be installed in wings or empennage.
Importance of Low Frequency ULB's :
LF-ULB's have a longer detection range as their frequency of emission is low compared to ULB's fitted with FDR/CVRs. This pinger signals can be detected from 13-22km range and has a maximum operational depth of 6,000m. The ULB mod itself contains the ULB DK180 Beacon, a mounting kit and an adapter plate.
Power source and life :
The battery of ULB is a single cell Lithium with 06 year life. The minimum voltage is 2.97 V and maximum is 3.5 V. This is designed in such a way that, once the unit is made in contact with water, it'll fill the circuit and the ULB unit gets activated and starts to send pinger signals.
Maintenance:
Maintenance Program is done on specific intervals to check the working of ULB's and also the checking of battery condition. These periodic inspection should be in accordance with the manufacturer's requirements.
How to locate ULB's :-
Upon contacting with water, ULB's circuit gets activated and then starts to send acoustic signals. These signals can be tracked either by ships or submarines which are deployed for search and rescue and also aircrafts with equipments to receive acoustic signals. The ships deployed for search and rescue has a towed pinger locator which is submerged in water which will scan for acoustic signals. Ship's onboard analyser will analyse the data which the towed pinger locator gives and finds the distress signal from ULB. If the signal is received and confirmed, they'll send underwater robotic submarines to retrieve the Black Box.
For this to happen, the investigation team should be knowing the last known position of the aircraft before it crashes to the sea. After studies, investigation team will locate the possible crash zone with the help of different parameters ; but the ocean is mysterious, its strong currents can even carry the crashed aircraft to other locations which, investigators may find hard to locate.
ULB : Underwater Locator Beacon
FDR : Flight Data Recorder
CVR : Cockpit Voice Recorder
Images : Google
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