Administrators overseeing the insolvency of collapsed electric vertical take-off and landing (eVTOL) developer Lilium say they have yet to receive key documentation from a would-be buyer of the firm’s assets.

But that could be the least of the challenges for Dutch-registered Ambitious Air Mobility Group (AAMG), which emerged in early August as the latest in a long line of suitors for Lilium.

AAMG – which had previously placed an order for 16 Lilium Jets – on 8 August said it hoped to lead a “revival effort” of a development programme that has been on ice since Lilium’s closure in February this year.

To continue the development of the Lilium Jet, AAMG says it aims to acquire Lilium’s core intellectual property, facilities and test assets.

It claims to be backed by €250 million ($291 million) of committed capital, plus with access to a further €500 million “to take the project beyond the test flights of MSNs 1&2”; partners in the project include Airmobility Inc of Japan and “a top 50 Dutch bank”.

AAMG has already made some progress, announcing on 14 August that it had signed a rental agreement for facilities at Lilium’s Oberpfaffenhofen airport base in southern Germany.

It also called on Pluta, the financial firm handling the insolvency of Lilium GmbH and Lilium eAircraft GmbH – the two German operating companies – to sign a draft asset purchase agreement that would allow it to “review the asset details [and] finalise transaction terms”.

Among the “concrete actions” AAMG says it has taken in recent weeks is to provide “confirmation of its banking relationships to the administrators”.

But Pluta says key documents are yet to be disclosed: “The requested bank guarantee has not yet been submitted.”

Pluta says it is “conducting discussions and negotiations with interested parties regarding the sale of Lilium as a whole or the sale of individual assets”.

It is unclear how many potential bidders are lined up, although FlightGlobal understands there is only one party interested in the entire business.

“We fully appreciate that the events leading to Lilium entering administration have been challenging for all involved,” says Dr Robert Kamp, chief executive at AAMG.

“However, providing a draft asset purchase agreement to a qualified and committed potential buyer carries no cost or risk to the administrators, and is a necessary step to enable progress.”

Besides securing Lilium’s assets and intellectual property, AAMG says one of its aims is the “retention and rehiring of key technical and certification teams”.

But it is doubtful how achievable that goal is: since Lilium’s closure many staff have found work elsewhere, notably at rivals in the eVTOL space, or given the multi-national nature of its workforce, have moved back to their home countries.

Lilium had also never moved beyond flights of its subscale ‘Phoenix’ demonstrators and it is uncertain how far ground testing of MSN1 had advanced.

MSN2 – the first flight-test aircraft – was still in final assembly when the companies entered insolvency in October last year and little progress was made during the months of upheaval that followed, including the abortive sale to would-be rescuer Lilium Aerospace.

Indeed, photographs obtained by FlightGlobal in June show the prototype was far from complete, with its propulsion system still to be installed.

Ultimately, however, the biggest challenge for AAMG may be one of physics. The Lilium Jet’s architecture causes high levels of disc loading in the propulsion system. While small-diameter fans boost cruise efficiency, it means the aircraft is particularly power-hungry during vertical take-offs and landings.

One senior former employee – who spoke to FlightGlobal on condition of anonymity – said Lilium had essentially built a “flying battery”.

The “very big” mass fraction of the battery system would also limit the payload to four passengers, they said, far from the six or seven envisaged, with related reductions in speed and range performance too.

Lilium had opted to forgo building a prototype of the Lilium Jet and would instead move straight to flight tests of what it said would be a certification-conforming asset.

However, this strategy was “hurting Lilium a lot”, the source says, as it inevitably restricted the fine-tuning of the system that would be needed ahead of certification.

Any last-minute changes, particularly those related to energy reserves, would “have a compounding effect” across the aircraft, they say, adding weight as components were sized up accordingly.

Although Lilium had been aiming for a first flight in 2025, another source says the programme was “very far behind where management thought we were”.

They also criticised the absence of a prototype in the programme: “This grand plan that the aircraft that would achieve first flight would also go towards certification and then production is ludicrous from an engineering point of view.

“With any development programme, the minimum viable product that you get doing the thing you want it to do is never going to be the one that enters production.”

In any case, they estimate that even if the programme had continued without the interruption of the insolvency, the best outcome for a first flight would have been a “short hop to get something off the ground”.

A third source says they shied away from accepting a job with Lilium due to problems posed by certification requirements relating to the transition from vertical to horizontal flight.

“There were really big technical challenges with it that I thought could not be reliably solved,” they add.