Air India Express Guwahati-Kolkata Flight Delayed 18 Hours Due to Technical Glitch

Operating Costs of a Boeing 787-9 Dreamliner Per Hour in 2026 The Boeing 787-9 Dreamliner is widely recognized as a premier long-haul aircraft, valued for its fuel efficiency and extended range. However, establishing a definitive hourly operating cost for the 787-9 is challenging due to the variability of numerous factors. These include fluctuating fuel prices, maintenance agreements, crew wages, airport fees, aircraft utilization rates, and differing ownership models, all of which significantly influence overall expenses. Estimated Hourly Costs and Variability Industry estimates for 2026 indicate that the variable operating cost of a Boeing 787-9 will range between $13,000 and $14,000 per flight hour. This estimate generally encompasses fuel, maintenance, crew salaries, ground handling, and navigation fees. When fixed costs and ownership-related expenses—such as depreciation, financing, or leasing—are factored in, the total hourly cost can escalate to between $15,500 and $22,000. These figures are highly sensitive to the specific operational practices and business models employed by individual airlines. It is important to emphasize that no universal hourly cost exists for the 787-9. Airlines operating longer routes with high utilization rates may achieve lower per-hour costs compared to those flying shorter sectors with more frequent ground time. Variations in maintenance contracts, labor agreements, airport networks, and financing arrangements further differentiate the cost structures among operators. For instance, JetHunter estimates variable operating expenses at approximately $13,160 per flight hour, though this figure is contingent on particular fuel price assumptions and should be regarded as a reference rather than a definitive benchmark. Fuel Costs and Market Challenges Fuel remains the largest and most volatile component of the 787-9’s operating costs. Boeing highlights that the aircraft’s advanced aerodynamics, modern engines, and composite materials contribute to up to 25% better fuel efficiency compared to older models. This efficiency is especially critical for ultra-long-haul routes such as London to Perth or San Francisco to Singapore. Despite these advantages, fuel expenses can still account for roughly $7,000 per flight hour, and any increase in global fuel prices could substantially raise this cost. Looking ahead to 2026, rising fuel prices pose a significant challenge that could markedly increase operational expenses for airlines. In response, carriers may adjust ticket pricing, optimize route networks, or pursue alternative, more fuel-efficient aircraft to manage costs effectively. Additionally, airlines might negotiate more favorable supplier contracts or reallocate capacity to more profitable routes to mitigate financial pressures. Regulatory developments are also expected to impact the cost environment. For example, proposed regulatory measures in Russia aimed at tightening criteria for airlines seeking international routes could affect operational flexibility and cost structures, particularly for carriers operating in or transiting through affected regions. Conclusion While the Boeing 787-9 Dreamliner offers substantial economic and operational benefits, its hourly operating cost in 2026 will be shaped by a complex interplay of fuel prices, operational strategies, and evolving regulatory frameworks. Airlines will need to maintain agility and adapt to both market dynamics and regulatory changes to sustain profitability on long-haul routes.

Cabinet Urged to Form Interagency Group on Aircraft Leasing Taxation The Cabinet of Ministers of Ukraine faces urgent calls to establish an interagency working group to address the contentious issue of aircraft lease payment taxation. This matter has drawn significant attention within the aviation sector following the Economic Security Bureau’s recent interpretation of leasing operations as royalty payments. This reinterpretation has triggered investigations into at least five airlines accused of failing to pay royalties on leased aircraft and helicopters. Government Response and Industry Concerns Volodymyr Kreidenko, Deputy Chairman of the Verkhovna Rada Committee on Transport and Infrastructure, underscored the government’s authority to coordinate relevant state bodies in resolving this issue. He emphasized that convening such a platform is a direct responsibility of the Cabinet, given its executive mandate. Industry representatives, speaking at a recent roundtable, highlighted increasing pressure from the Economic Security Bureau and urged the Cabinet, alongside the Ministry of Finance, State Tax Service, and other agencies, to develop a unified and clear position on the taxation of aircraft lease payments. They warned that without definitive guidance grounded in both Ukrainian and international law, Ukraine risks jeopardizing a high-tech sector that continues to operate, fulfill international contracts, and contribute to the state budget despite ongoing conflict. Kreidenko proposed that the working group include representatives from key government bodies such as the Ministry of Finance, State Tax Service, Economic Security Bureau, Ministry for Communities and Territories Development, and the State Aviation Service. Crucially, he also advocated for the inclusion of Ukrainian aviation industry representatives and members of parliament from relevant committees to ensure effective oversight and practical outcomes. Broader Context and Legislative Considerations The debate over aircraft leasing taxation in Ukraine mirrors broader global challenges faced by the aviation industry. Navigating complex regulatory frameworks and ensuring compliance with international tax laws remain critical as the global aircraft leasing market evolves. Major manufacturers like Airbus and Boeing are closely monitoring regulatory developments, while the emergence of Chinese leasing firms is reshaping market dynamics across Asia. This intensifying competition is prompting countries worldwide to adapt their leasing policies to maintain competitiveness. Additionally, international law firms specializing in aircraft finance and leasing, such as Smith Gambrell, are expanding their expertise, potentially influencing market practices and responses to new taxation frameworks. Kreidenko noted that the Parliamentary Committee on Transport and Infrastructure lacks the jurisdiction to resolve the tax classification issue independently, as it falls under the remit of the tax committee. He recommended that, alongside the interagency group’s efforts, the Ministry of Finance should issue a generalized tax consultation on the taxation of aircraft operating lease transactions. Such a measure, he argued, would provide the fastest and most effective unified clarification, taking into account international treaties on double taxation. Should administrative measures prove inadequate, Kreidenko indicated that the Verkhovna Rada might need to consider targeted amendments to the Tax Code. He also suggested that the Business Ombudsman Council could serve as an additional mechanism to safeguard business interests as Ukraine navigates these complex regulatory and market challenges.

Eight Killed in Twin-Engine Cessna Crash Near Remote Alaska Radar Site A twin-engine Cessna charter plane crashed near a remote radar station in western Alaska on Thursday, resulting in the deaths of all eight people on board, according to the Alaskan Command. The aircraft, operated by Security Aviation, was traveling from Anchorage to Cape Newenham when it went down near the Cape Newenham Long Range Radar Site, approximately 40 miles south of Goodnews Bay. Details of the Crash and Response Efforts The National Transportation Safety Board (NTSB) and the Federal Aviation Administration (FAA) have launched a joint investigation into the incident. Clint Johnson, chief of the NTSB’s Alaska office, confirmed that the plane was carrying two pilots and six passengers. The crash occurred on land close to Cape Newenham Airport, an Air Force airstrip that serves as the primary access point to the radar station. Following a report of an “aircraft incident” near the radar site, the Alaska Rescue Coordination Center initiated a search-and-rescue operation. Alaska State Troopers and the Rescue Coordination Center responded promptly to the scene. Authorities have not yet disclosed the identities of those involved. Aviation Safety Concerns in Alaska This tragic event highlights ongoing concerns about aviation safety in Alaska, a state known for its challenging flying conditions and a history marked by fatal crashes. Previous accidents in the region have prompted scrutiny of operational practices, including issues related to aircraft weight limits and the sufficiency of FAA oversight. Officials have stated that further information will be released as the investigation progresses. The cause of the crash remains under active review.

American Airlines to Expand Fleet and Upgrade Cabins in 2026 American Airlines, one of the world’s largest carriers by fleet size, is set to undertake a significant expansion and modernization of its aircraft fleet in 2026. With a history dating back to the 1920s and a network spanning nearly 350 destinations across more than 60 countries, the airline currently operates over 1,000 aircraft. Over the coming years, American Airlines plans to take delivery of 280 new planes, including 102 Airbus A321neos, 44 A321XLRs, 115 Boeing 737 MAX 10s, and 19 Boeing 787-9 Dreamliners. Delivery Schedule and Fleet Expansion For the year 2026, the airline anticipates receiving 48 new aircraft, according to its latest Fleet Fact Sheet. This follows the acceptance of 22 aircraft so far this year, comprising a mix of 737 MAX 8s, A321neos, and A321XLRs. The remainder of the year will see the arrival of 15 additional A320 family aircraft and 11 Embraer E175s. This revised figure is slightly lower than earlier projections, which initially estimated 55 deliveries for 2026 before being adjusted to 49 and now 48. The downward revision is primarily attributed to supplier delivery delays. A significant alteration in the delivery timeline concerns the Boeing 787-9 Dreamliner. Although American Airlines is awaiting 19 Dreamliners and holds options for 28 more, recent schedule adjustments have postponed one 787 delivery from 2026 to 2027, while advancing two originally slated for 2028. Consequently, the airline does not expect to receive any 787-9s in 2026. These changes reflect ongoing supply chain challenges at Boeing, which has experienced production rates below targets in early 2026. Cabin Upgrades and Competitive Positioning Beyond fleet expansion, American Airlines is embarking on a major cabin upgrade program aimed at enhancing its competitive stance, particularly against rivals Delta and United. Beginning in 2028, the airline will retrofit existing aircraft and equip new deliveries with advanced seatback entertainment systems featuring 4K displays and USB-C charging ports. This initiative responds to rising passenger expectations and competitive pressures, as Delta and United currently offer seatback screens on more than 900 and 800 aircraft, respectively. In addition, American Airlines plans to increase the number of premium seats across its narrowbody fleet to attract higher-yield customers. The airline will also refurbish its Boeing 787-8 Dreamliners with new business-class suites, further elevating its premium product offering. These strategic investments are designed to reinforce American Airlines’ position as a leading premium carrier and to narrow the profitability gap with its main competitors. Despite the adjustments to its delivery schedule, American Airlines remains committed to modernizing its fleet and enhancing the passenger experience as part of its long-term strategy for growth and competitiveness.

Delta Flight Returns to Atlanta Airport Following Engine Malfunction Emergency Landing After Mechanical Issue A Delta Air Lines flight was compelled to return to Hartsfield-Jackson Atlanta International Airport on Thursday evening after encountering engine trouble shortly after departure. Flight 1518, a Boeing 737-900 carrying 173 passengers and bound for Raleigh, North Carolina, safely landed back at the airport after the flight crew identified a mechanical problem with the aircraft’s right engine. The affected plane was immediately taken out of service for a thorough inspection and necessary maintenance. Delta is currently rebooking all passengers on alternative flights to their intended destination. Airline Response and Operational Impact A Delta spokesperson underscored the airline’s prioritization of safety, stating, “Nothing is more important than the safety of our people and customers.” The company also issued an apology to travelers for the disruption caused by the incident. This event presents several operational challenges for Delta, including potential delays in maintenance schedules as the aircraft undergoes repairs. Passenger dissatisfaction is another concern, given the interruption to travel plans. Furthermore, the incident is likely to attract increased scrutiny from aviation regulators investigating the mechanical fault. Broader Implications for Delta Beyond immediate operational effects, such incidents can influence market perceptions of the airline. Investor confidence may waver temporarily, potentially impacting Delta’s stock performance. Competitors might also leverage the situation to highlight their own service reliability records. Delta has reiterated its commitment to safety and customer service as it addresses the consequences of the engine malfunction. Efforts are underway to minimize inconvenience for affected passengers while ensuring compliance with all safety protocols. This story is ongoing, and further updates will be provided as more information becomes available.

Samoa Airways Undertakes Recovery of Damaged DHC-6-300 Aircraft Samoa Airways (OL, Apia Faleolo) is actively engaged in the recovery of its damaged DHC-6-300 aircraft, registration 5W-FAY (msn 690), following a runway excursion at Fitiuta on July 28, 2026. Rather than opting for temporary repairs and a ferry flight to its maintenance base in Apia Faleolo, the airline has chosen to dismantle the aircraft on site. Engineers from Unity Aviation will conduct a thorough technical assessment to determine whether repairs can be completed in Samoa or if the aircraft will require more extensive work in Canada. The recovery operation, which began with the aircraft’s removal from the airport on August 14, is expected to take up to three months. Operational Challenges Amid Industry Changes The grounding of 5W-FAY has rendered approximately one-third of Samoa Airways’ fleet inoperable, underscoring the operational vulnerabilities faced by smaller regional carriers. This incident occurs amid significant shifts in the regional aviation market, including the relaunch of the DHC Sherpa airlifter, which is altering competitive dynamics and potentially impacting the market position of aircraft such as the DHC-6-300. Regional competitors like CemAir have demonstrated resilience and strategic agility, successfully navigating growth despite prevailing industry challenges. Broader trends within the aviation sector are also shaping Samoa Airways’ recovery strategy. Major carriers, including Copa Airlines, are projecting increased capacity, while others like SunExpress are embracing flexible and sustainable growth models. The ongoing recovery from the COVID-19 pandemic has highlighted the critical importance of adaptability, as evidenced by operational disruptions experienced by airlines such as Aerodiana. These evolving conditions are likely to influence both the technical repair decisions and the commercial considerations surrounding the restoration of Samoa Airways’ fleet. As the airline awaits the outcome of the technical evaluation, it faces the complex task of balancing immediate operational demands with the broader, evolving dynamics of the regional and global aviation markets. The decision on whether 5W-FAY can be repaired locally or must undergo more extensive work abroad will carry significant implications for Samoa Airways’ competitiveness and resilience in an increasingly fluid industry environment.

Man Ingested by Frontier Airlines Engine Highlights Denver’s Persistent Airfield Security Challenges On May 8, a fatal incident at Denver International Airport (DEN) brought renewed attention to the airport’s ongoing airfield security vulnerabilities. Matthew Mott, who gained unauthorized access to the secure airfield, was tragically ingested by the engine of a Frontier Airlines Airbus A321neo during its takeoff roll. The collision caused a loud impact, resulting in an engine malfunction and fire. Despite the severity of the event, all passengers and crew were safely evacuated and rebooked on a replacement flight. Authorities later confirmed Mott’s death at the scene, ruling the incident a suicide. A Pattern of Security Breaches at Denver International This incident marks the sixth known airfield security breach at Denver International Airport over the past three years, underscoring persistent challenges in maintaining perimeter security. Previous breaches have varied in nature, including individuals breaching perimeter fences, sitting on taxiways, or attempting to cross the airfield on foot. One notable case involved a trespasser claiming to be “walking to Texas,” a journey of over 900 miles. While none of these prior incidents resulted in fatalities, the recurrence of such breaches raises serious concerns about the effectiveness of current security measures. Annmarie Heth, assistant professor of aviation and aerospace sciences at Metropolitan State University of Denver, emphasized that although fatal outcomes remain rare, determined individuals can sometimes circumvent even advanced security protocols. The frequency of these intrusions at one of the nation’s busiest airports has intensified scrutiny of Denver’s detection systems and response strategies. Implications for Aviation Security and Industry Response The May 8 tragedy has placed the aviation industry under heightened pressure to reassess airfield security protocols. Regulatory agencies are expected to increase oversight, potentially leading to operational disruptions as airports and airlines implement enhanced security measures. Frontier Airlines, which has recently focused on fleet rightsizing and operational efficiency, now faces intensified public and regulatory scrutiny regarding the safety and reliability of its fleet and procedures. Compounding the challenge is the absence of a comprehensive national database for airport security incidents. While the Federal Aviation Administration (FAA) monitors runway incursions—defined as unauthorized presence of aircraft, vehicles, or individuals on runways—only two of Denver’s six recent breaches are recorded in FAA data. In total, DEN has documented 37 incidents involving unauthorized vehicles and pedestrians over the past two years, highlighting gaps in reporting and tracking. As investigations into Mott’s death continue, calls are growing for more robust and standardized reporting mechanisms for airfield security breaches nationwide. With public confidence at stake, the Denver incident may serve as a catalyst for industry-wide reforms in security standards and operational practices.

The Advantages and Disadvantages of Owning Versus Leasing a Private Jet Private jets have long been emblematic of luxury and exclusivity, yet access to them has expanded significantly in recent years. Between 2000 and 2022, the global private jet fleet more than doubled, increasing from 10,000 to over 23,000 aircraft. Demand continues to rise sharply, with over 8,000 new jets anticipated in the coming decade and 3.6 million business jet flights recorded worldwide in 2024—a 30% increase compared to 2019. Leading companies such as NetJets, VistaJet, and Flexjet are responding to this surge by prioritizing sustainability, personalization, and cutting-edge technology. Privacy, Comfort, and Flexibility For high-net-worth individuals and corporations, commercial air travel often fails to meet the demands of time efficiency, flexibility, and privacy. Private jet ownership offers a level of control unattainable through commercial airlines. Owners have the authority to determine exactly who is on board, a critical advantage for executives, celebrities, and others requiring confidentiality. Additionally, cabin customization is a significant benefit, allowing owners to tailor everything from seating arrangements and lighting to Wi-Fi connectivity and in-flight dining according to personal preferences. Flexibility remains a defining feature of private aviation. Owners can fly directly to smaller regional airports, depart according to their own schedules, and alter routes mid-flight if necessary. Unlike commercial airlines, private jets are not subject to blackout dates or competition for seats. Speed is another advantage; most private jets cruise between Mach 0.78 and 0.81 (approximately 515–621 mph), with high-performance models such as the Gulfstream G650 and Bombardier Global 8000 pushing these limits even further. The High Cost and Commitment of Private Jet Ownership This level of control and convenience, however, comes at a considerable cost. The largest private jets can exceed $400 million in price, while smaller models like the HondaJet Elite start at around $5.5 million. Mid-size jets such as the Bombardier Global 5000 typically range from $35 million to $60 million. Although purchasing a used jet may reduce upfront expenses, it often necessitates additional investment in upgrades or refurbishments. Beyond the initial purchase, ownership entails substantial ongoing costs. Annual operating expenses—including maintenance, repairs, hangar fees, insurance, and crew salaries—generally fall between $500,000 and $1 million. Recent developments have introduced new financial pressures; for instance, Starlink’s private jet internet service recently doubled its monthly fee for the Aviation Global Unlimited plan and launched a new Regional plan with limited coverage. Industry responses have varied, with Flexjet absorbing these increased costs for its fractional owners, while Nicholas Air has publicly criticized the price hikes. Emerging Trends: Return on Investment and Shared Luxury As operational costs escalate, business leaders are increasingly evaluating the return on investment (ROI) of private aviation with a focus on productivity and operational efficiency rather than solely on acquisition costs. Concurrently, the trend of private jet sharing is gaining momentum. Affluent travelers are increasingly opting for shared luxury flights, seeking to enjoy the benefits of private aviation without bearing the full financial burden of ownership. Private jets continue to offer unmatched privacy, comfort, and flexibility, but these advantages come with significant financial and operational commitments. As the industry evolves in response to new technologies, rising costs, and changing traveler preferences, prospective owners and lessees must carefully assess the true value of private aviation, balancing luxury and convenience against the challenges and expenses involved.

Former Spirit Employees Challenge Google’s AI Data Acquisition Over Privacy Concerns Former employees of Spirit Airlines have voiced significant concerns regarding a recent agreement that would transfer a substantial volume of the defunct airline’s business records to Google for use in training artificial intelligence models. The Association of Flight Attendants-CWA (AFA), representing thousands of former Spirit staff, filed a formal objection on Tuesday in the U.S. Bankruptcy Court for the Southern District of New York. The union argues that the $10 million deal jeopardizes employee privacy and should be halted. Spirit Airlines, which ceased operations earlier this year following its second bankruptcy, agreed to sell its data to Google after the tech giant outbid AI startup Mercor. The arrangement requires Google to collaborate with a third-party “deidentification agent” to ensure that no consumer information is included in the dataset, in compliance with the California Consumer Privacy Act (CCPA). However, the AFA contends that these safeguards do not adequately protect employee records, which encompass sensitive materials such as business travel logs, crew training files, tax documents, and over 100 million emails. AFA attorney Charles Rubio emphasized in the court filing that while customer data is shielded, “no comparable screen has been applied to the employment record that this transaction actually conveys.” Rubio warned that even in the absence of names, the data could expose details about employee grievances, training performance, internal investigations, compensation adjustments, and communications related to management or union affairs. The union is urging the court to reject the sale unless all flight attendant information is explicitly excluded from the transfer. Following the objection, the bankruptcy court postponed approval of the $10 million transaction, according to The Wall Street Journal. A Google spokesperson responded to the concerns by stating, “We will not receive any personal information from this dataset. Any data we receive will be rigorously scrubbed of any personally identifiable information by a third party before receipt.” Nevertheless, the dispute underscores growing tensions over how technology companies acquire the vast datasets necessary to develop advanced AI systems. Broader Implications for AI Development and Privacy Google’s pursuit of Spirit Airlines’ data reflects a wider industry trend. As AI models become increasingly sophisticated, technology giants are seeking new and often controversial sources of training data, sometimes at the expense of employee privacy and ethical standards. With much of the publicly available internet content already harvested for AI training, companies are turning to alternative datasets, raising complex questions about consent and data protection. While synthetic data has been proposed as a potential solution, it presents its own technical and ethical challenges. Google’s AI ambitions have recently encountered setbacks. The company’s Gemini 3.5 Pro model has missed several scheduled release dates, prompting internal restructuring within its AI division. Meanwhile, competitors such as Anthropic and OpenAI continue to advance rapidly, intensifying the competition for high-quality training data. Additionally, Google’s increased capital expenditure on its cloud computing division has sparked investor concerns regarding the long-term sustainability of its AI investments. As the bankruptcy court deliberates on the fate of Spirit’s data, this case has emerged as a focal point in the ongoing debate surrounding privacy, ethics, and the future trajectory of artificial intelligence development.

China Certifies Pilotless Air Taxi for Export; Sri Lanka Becomes First Buyer EHang Holdings Limited (Nasdaq: EH) has announced a major advancement in the global deployment of autonomous air taxis with the launch of its Global Fast Track Program. Unveiled on August 19, this structured, four-phase initiative is designed to assist foreign civil aviation authorities in evaluating and authorizing pilotless electric vertical take-off and landing (eVTOL) operations. Sri Lanka’s Civil Aviation Authority and Ministry of Ports and Civil Aviation have become the program’s first adopters, targeting provisional commercialization within four months, subject to the completion of all necessary safety, technical, and regulatory approvals. EHang’s approach extends beyond the mere sale of aircraft; it capitalizes on the company’s extensive regulatory experience across 23 countries, offering this expertise as an exportable service. For regulators hesitant to develop new frameworks for autonomous aviation from the ground up, EHang provides a streamlined alternative: validate its aircraft, which already holds certification from China’s Civil Aviation Administration (CAAC), thereby significantly reducing the regulatory burden. The Only Certified Pilotless eVTOL Stack At the core of EHang’s offering is the EH216-S, the world’s first pilotless, human-carrying eVTOL to receive a comprehensive certification package from the CAAC. This includes the type certificate, production certificate, and standard airworthiness certificate. In March 2025, two EHang operators were granted China’s first Air Operator Certificates for pilotless passenger eVTOL commercial service, initiating ticketed flights in Guangzhou and Hefei. This full certification suite—covering type, production, airworthiness, and commercial operating authority—constitutes the regulatory foundation that EHang now proposes to export to other countries. EHang contends that by validating an already-certified aircraft for local airspace, rather than conducting a full regulatory assessment from scratch, foreign authorities can reduce the timeline from initial inquiry to operational trials from several years to mere months. Hu Huazhi, EHang’s Founder, Chairman, and CEO, described the program as a “systemic advance” that transforms regulatory exploration into tangible progress. Four-Phase Global Fast Track Program The Global Fast Track Program condenses years of regulatory engagement into a four-stage process. The first phase involves establishing a regulatory workflow and validation pathway tailored to the host country’s aviation framework. The second phase focuses on site selection, infrastructure development, and deployment of operational systems. The third phase consists of validation flights conducted within a designated sandbox zone under agreed safety standards. The final phase is the commercial launch, contingent upon receiving operational approval. This framework draws on practical experience from early sandbox projects in Thailand, Qatar, and Switzerland. Notably, Thailand’s Advanced Air Mobility Sandbox, launched in October 2025 in Bangkok, serves as the closest operational precedent, although it has yet to secure full commercial authorization. Opportunities and Challenges Ahead China’s certification of a pilotless air taxi for export, with Sri Lanka as the inaugural buyer, represents a significant milestone for the autonomous aviation industry. However, it also presents considerable challenges. Regulatory hurdles remain substantial in international markets, as each country’s aviation authority must rigorously assess and validate the technology within its own operational context. Additionally, EHang faces competition from established aviation companies that may accelerate their autonomous flight initiatives or pursue strategic partnerships in response. The market is expected to witness increased interest from other potential buyers alongside intensified scrutiny from global aviation regulators. As EHang’s regulatory model gains momentum, competitors are likely to expedite the development of comparable technologies, heightening the race to commercialize pilotless air taxis on a global scale. Sri Lanka’s adoption positions the country as a regional pioneer in autonomous air mobility, with plans to deploy the technology along tourism routes. The forthcoming months will be critical in determining whether EHang’s regulatory framework can fulfill its promise of rapid, safe, and scalable deployment beyond China’s borders.