* Flannery to take over as CEO on Aug. 1, chairman on Dec. 31
* Shares have fallen 30 pct during Immelt's tenure
* Stock rises about 4 percent (Recasts, adding quote and detail on timing of GE succession plan)
June 12 (Reuters) - General Electric Co on Monday named John Flannery as its next chief executive, taking over from Jeff Immelt who is stepping aside after 16 years as the head of the conglomerate, which he helped steer through the financial crisis but is now worth a third less than when he took over.
GE said John Flannery, the head of its healthcare unit, will replace Immelt as CEO, effective Aug. 1, and as chairman after Immelt retires on Dec. 31.
"I want to start with a fresh look around the company overall and I think with a sense of urgency. There's so many things we do well and have always done well and there's clearly some areas we need to improve on and improve on quickly. No one's happy with the stock price right now or some of the cash pictures that we have had," Flannery said at a Facebook live session.
The company's shares were up 3.6 percent at $28.97 as Flannery's appointment to the top job ended a six-year long succession planning program.
Immelt, 61, who took over from Jack Welch in 2001, oversaw the divestment of its massive lending unit GE Capital and TV network NBCUniversal, shifting the conglomerate's focus away from finance and toward healthcare and manufacturing. He also bet on developing digital technologies to transform the company's factories.
But his efforts to refocus the company on high-margin businesses failed to energize the stock price.
Since Immelt became CEO in 2001, GE's shares fell 30 percent, while the S&P 500 index more than doubled. That underperformance had some pressing for more urgency from Immelt.
Activist investor Nelson Peltz's Trian Fund Management bought a stake in GE in October 2015, the largest single investment the firm had ever made, and now worth about $2 billion. Trian immediately pushed for asset sales and cost cuts. Trian declined comment.
GE said Immelt's departure was not triggered by outside influences, and that its board set the summer of 2017 for Immelt's departure as far back as 2013.
Stifel analyst Robert McCarthy said the timing was not surprising because of the serial underperformance of the stock and "investor fatigue with management's continued perceived ungainly portfolio actions".
During Immelt's tenure, GE bought French peer Alstom's power business and announced a deal to acquire oil and gas company Baker Hughes, while jettisoning the NBC unit and even its famed appliances division.
Still, the company - the oldest surviving member of the Dow Jones Industrial Average - has struggled to boost sales significantly in the past few quarters. In particular, the company's cash flow has been a cause for concern.
Flannery, 55, who is currently president and CEO of GE Healthcare, joined GE Capital about three decades ago. At the lending unit, he focused on leveraged buyouts and later led the corporate restructuring group.
He has led GE's India business, its equity business in Latin America and the GE Capital business for Argentina and Chile.
Flannery has also led the turnaround of the healthcare business, increasing organic revenue by 5 percent and margins by 100 basis points in 2016, GE said in a statement.
The company said Kieran Murphy, president and CEO of GE Healthcare Life Sciences, will replace Flannery. (Reporting by Arunima Banerjee in Bengaluru; Editing by Saumyadeb Chakrabarty and Bernard Orr)