Indonesia's National Transportation Safety Committee (KNKT) said its probe into the crash of Lion Air Flight JT610 may take up to six months, as the search for the black box flight recorders continued into its third day yesterday.
A preliminary report of the investigations, however, will be released in about a month, said KNKT chief Soerjanto Tjahjono.
A complete study may take up to six months, he added.
Dr Soerjanto's comments yesterday came amid widespread anticipation that divers might have recovered a black box from the ill-fated flight, after news broke that a part of the fuselage was found in the search area earlier in the day.
Indonesian Armed Forces chief Hadi Tjahjanto had said a large object, suspected to be a key part of the Boeing 737 Max 8 jet that crashed into the Java Sea on Monday morning, was detected by search and rescue teams.
"We strongly believe that we have found a part of the JT610 fuselage," he told reporters early yesterday morning at the Jakarta International Container Terminal in Tanjung Priok, where a command centre for search and rescue operations had been set up.
Although Dr Soerjanto could not confirm that the fuselage had been found, he agreed with Air Chief Marshal Hadi that the black boxes could be located soon.
This was because search teams had detected consistent "ping" signals with 0.9-second intervals from what could be the flight recorders.
Dr Soerjanto said "70 per cent" of the search had been completed.
"After finding the black boxes, we will evaluate, analyse and discuss with the manufacturer about the (aircraft) system and why (the crash) occurred," he added.
Flight JT610, which was bound for Pangkal Pinang in Bangka Belitung Islands province, plunged into the Java Sea minutes after take-off from Soekarno-Hatta airport.
Efforts to locate survivors and the black box flight recorders in the waters off Karawang, West Java, have not been successful so far.
While all 189 people on board are feared dead, at least one family received some closure after police confirmed the identity of a 24-year-old passenger from her remains.
Police Brigadier-General Hudi Suryanto said they managed to match her fingerprints to government records, identifying her as Indonesian civil servant Jannatun Cintya Dewi.
"We have examined 48 body bags of human remains and we could identify one victim through primary identification, which comprises fingerprints and dental records," said Brig-Gen Hudi, who heads the police unit that manages the Automated Fingerprint Identification System.
Her partial body, which had five fingers on a right hand intact, was in one of 24 body bags received by the police on Tuesday, he said, adding: "The condition of the remains found was better than most, so the identification process was somewhat easier."
Ms Cintya was on the flight to Pangkal Pinang for work with two colleagues from the Ministry of Energy and Mineral Resources.
Lion Air pledged to assist her family with their needs and provide compensation.
Representatives from Boeing and the US National Transportation Safety Board will be meeting KNKT officials today.
Yesterday, Transportation Minister Budi Karya Sumadi said he has ordered Lion Air to temporarily discharge its technical director to allow him to focus on assisting in the KNKT investigations.